The following is an except from this excellent web site. The site has since disappeared so I'm glad I saved this page. There is much discussion about this on the web both for and against. There seem to be a number of non-believers out there. I can testify that it is happening. This foam is nasty stuff and corrodes anything it touches. There are two types of keyboard blocks in these Hammonds. The earlier ones use white felt and the problem ones use sponge which is now black. This can actually be seen if you lift the keyboard block up by undoing the four securing bolts and tilting it up from the front. You need to look from the front into the bottom of the metal box that holds the contacts. You should be able to see the felt or sponge. If it's white felt, screw it back together and have a long and happy life together, if it's sponge get it fixed.

Quote "Of all the strange myths that have grown up around Hammond organs over the years, there is one which is particularly illogical and decidedly unhealthy. It is this; that a Hammond organ is Immortal, and will continue to Live for all Eternity. The belief is that no matter how mistreated, or under-serviced, it will somehow manage to survive just a few more gigs. And if it has been oiled once or twice since manufacture, and has been occasionally polished, then it will positively live for ever. This document is concerned with the increasing number of serious technical problems encountered by us in our renovation work. However well equipped our workshop may be, we are constantly obliged to wrestle with new difficulties. New renovation techniques have to be developed, which require specially made tools and machines, as well as hand made spare parts. The ever increasing demands on the Hammond renovation specialist is however only one aspect of the present situation; another aspect is to make Hammond owners aware of the problems to be overcome, if their organs are to survive. In this respect, there appears to be little or no help to be sought elsewhere on the internet, where information is usually what appears in old Hammond publicity material and service manuals. It is easier to understand why this 'keep-me-happy information' is so abundant, when one realises that the alternative is to consider the alarming nature of the truth. The small, unattended problems of the past became big problems, and more recently have become acute. In just a few years from now, most of the important models will have become so decrepit that they will be unplayable. Then, after a further period of neglect they will finally be discarded. It is simple to summarise the present day situation for models such as the A-100, the C-3 and the mighty B-3.
They are dying.

Mad Cow Disease

When production of the B-2 gave way for the B-3, Hammond made a change that was to prove fatal for the new model, after an incubation period of 40 years. It is like a disease that attacks the organ's brain, for thus could one liken the thousands of hair-fine resistance wires that connect the 1098 key contacts to the tone wheel generator. A long strip of self-adhesive dust excluder was attached to the inside of the angled protection plate covering the contacts from the rear, in order to prevent dust, dirt and other foreign material entering this very sensitive enclosure. From previously having being made of cotton felt, this strip was changed to an early form of foam rubber, which after 40 years has decayed into a black, sticky mass. Unfortunately, the products of decomposition are caustic, and the rotting strip is eating away the resistance wires where it is in contact with them. The lacquer insulation covering each wire has reasonable resistance to chemical attack, but having penetrated this protective layer, the process accelerates, and soon the wires are eaten right through. In no particular systematic order, certain footages on certain keys will cease to work, resulting from breaks in the resistance wires feeding the appropriate tones to those particular key contacts. One by one, more and more tones will disappear, making the job of reconnecting the ends become exponentially more difficult.

Caustic foam rubber residue on resistance wires

This magnified image, taken with special photographic equipment, should strike horror into the hearts of ABC owners. This is by no means a photograph of an exceptional case; every ABC organ that has been opened in our workshop during the last four years has looked like this. Using the match head for comparison, the thinness of the multitude of resistance wires can be appreciated. The different colours of enamel are codes indicating different specific resistances. The black bubbling mass at the bottom is the decomposing foam rubber. The caustic nature of this unpleasant substance reveals itself where a distinctive green tinge appears, as on the arching resistance wires that can be seen covered with it. Here, the protective enamel has finally succumbed to the aggressive chemical attack, hereafter the resistance wire itself is more easily eaten through. When attacked chemically, it is the copper constituent of the resistance wire alloy that produces the characteristic green colour, and such wires must always be replaced. On this particular manual, two wires were already eaten through, another wire disintegrated during the cleaning process and a fourth wire (the one shown in the picture) was so poor that it was removed and replaced. Organs are now turning up with many more than just four ruptured wires, and the situation is steadily deteriorating. There can be little doubt that what we term 'mad cow disease' is the greatest single threat to ABC organs, and it will be this, before anything else, that puts them in their graves.

The offending caustic strip on the inside of the covering plate. Note the indentation along the strip, where material has separated away and is now stuck to the resistance wires.

Both upper and lower manuals are affected on all models using the B-3 manual assemblies; A-100 & 105, B-3, C-3, D-100, RT-3, which we collectively term 'ABC' organs. This condition is slowly but certainly killing every ABC organ ever made - we have found caustic attack in varying degrees on every single ABC manual assembly that we have opened during the last four years. In several cases, wires have now been found eaten right through. The only cure is by prevention, whereby the manuals are removed from the organ, the cover plates are then removed from the manuals, and finally the strip is cleaned off from the cover plate and the wires. This process is one of the most complicated jobs imaginable; do not under any circumstances attempt it yourself. Job grade 5."

We know what we are, but know not what we may be - William Shakespeare