Advice needed for a Yamaha SY 1

I bought this Yamaha SY-1 very cheap - 400dkr (~$60) - and all was hunkydory untill I found that there is a problem with the envelope generator - a problem that is unfixable because those ass....not-so-nice-persons at Yamaha decided that it was a fantastic idea to cast a block of epoxy around the parts that are most likely to fail! According to the service manual that I found online the reason is to make sure everything inside the blocks has the same temperature. In other words to secure a stable operation. Personally I think the reason is that they didn't want competitors to see how they had designed their circuits. The somewhat similar Roland SH-2000 from the same age are much more repair-friendly and nothing is hidden there - and it is also quite stable to temperature changes. I made a temporary repair that isn't very good. So I would like to ask if anybody has an idea to what I should do to get it fully operational again? The music is something I made in 1997 (sorry about the tape noise) and is primarily played on Roland SH-2000. The other instruments are Roland CR-1000, Casio SA-1 and SA-3, and Bontempi KS-3400.