Last month I finally managed to acquire Rock Lobster of my own!
Unfortunately, battery has leaked badly:http://1drv.ms/1Dntm0N
This stuff found it's way even on some of the rear connectors -- no idea how it got there.
I removed the battery, gave it a good scrub with diluted vinegar and then started removing affected parts.
So far got the expansion connector off (replacement arrived yesterday).
Custom chips look fine, all chips with crap on them are standard 74 parts so ordered a bunch of those and sockets from eBay and AliExpress.
That's the easy bit.
However, on some parts of the motherboard it looks like it leaked under the clear coat. Most look unimportant (empty or just test points) but there are some areas where there are larger traces (around edges of the expansion cut out). The traces haven't been eaten through yet, but they will be if left like that.
I've never tried to restore motherboard affected with battery rot before. Anyone here done it before and can share some lessons learned?