The rectifiers (off board, and with heat sinks) were probably attempts at improvements on the notoriously underrated W02M rectifiers that are standard on most Oberheim products.  When these get too hot, which is not uncommon, they can start dropping out, causing glitches in the power supply.
I'd say, first determine if there are any problems with the power supply as things are now.  If the voltage measurements on all supplies are normal, I'd say leave it alone.  There are plenty of other things that could be causing your problems.