This unit had been powered off for many years, and although it looked nice once dusted off, oxidization had done its worst on key contacts, made sliders crackly etc. The brass section was not working, and the pitch slider was broken. I could not find a source for sliders, and ended up grafting a metal shaft onto the pitch control. The sliders are of a closed and sealed type, but thankfully (and surprisingly to me) injecting switch cleaner into screw holes in the slider cases banished the crackles.
Investigating the brass issue revealed cracks in a circuit board from impact, with a poor repair attempt in the past. I wire jumpered all bad and suspect circuit board traces such that if the crack grew a little then it would still work. The final issue was key contacts, and in the end I had to remove the buss-bars in order to clean them which is a major strip-down effort. The contact springs were really bad and had to be repeatedly treated using isopropryl as a cleaner. The results are pretty good, but the only way to get it to 100% would be to find new springs. Customer just loves it!