A downscaled D-50 (losing chorus and other fx, and pwm, but with 32voice voices instead of 16 plus more samples). Review notes that these sound punchier which isn't surprising given trimming of features and probably increased processing speeds. D20 adds 8 track sequencer.
Other than key cleanings and some dirty buttons I haven't seen much trouble with these machines. The one I recently got in the contacts were falling apart on. Most of them cracked around the contact and some had fallen out. I decided to turn it into a module :-).
Roland still stocks many parts for older instruments! You can always order them through your local Service Center and see what happens! Otherwise I have some parts also so don't hesitate to ask.
Contact Sound Doctorin'