Vintage Synth Repair

> Could you please describe (both for me and for all the people in the future who will be reading this sequence of postings) exactly what kind of damage that an old memory battery does to vintage synthesizers? Thank you.
 
Specifically the problem involves rechargeable NiCd batteries.  The more common lithium batteries shouldn't cause any trouble (not that I've ever seen, anyway).  Of course ordinary AA batteries can also leak and ruin your day, but these aren't usually mounted on circuit boards.
 
A few things that use these: Korg Polysix, Poly 61 and Trident, Siel DK 600, DK 700 and Expander, Roland CR-78, Kawai SX210 and SX240, PPG Wave series, Wersi, as well as lots of other old electronics.  Leakage in pinball machines seems to be particularly insidious, I guess because they can sit in storage for a couple decades while the battery works its magic.
 
Over time the (NaOH or KOH?) electrolyte leaks out, possibly encouraged by the recharging circuit.  Component leads corrode, circuit board traces turn black, solder turns to a powdery gray substance.  The damage can spread to a quite impressive area, though not all of it will need to be repaired.  The solder is especially a pain since it won't melt or allow new solder to adhere.  It can be very difficult to remove without actually drilling out all the vias and holes.   		 	   		  
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