I've used Apple Cider Vinegar to remove corrosion on a severely corroded Mac SE/30 metal chassis. It does a good job. I followed that up by spaying primer. It came out great! Good luck!
I use my SE/30 as a file trafficker to get data from my PowerMac 6500 to my Apple IIGS. The IIGS has a network card, but I don't know how to get AppleTalk to work with it. So I shuttle data from my 6500 to the SE/30, and copy data onto a 3.5" floppy to feed the IIGS. :D
Nice score! Those Transwarp GS cards go for a crazy amount online. Hoping we'll see a modern accelerator solution for the IIGS... given the interest in retro computing, it seems possible.
It sounds like the PSU needs a recap. I proactively did this on a Mac SE FDHD I purchased from Craigslist two years ago (for the princely sum of $30!). JDW's excellent guide on YT walked me through the whole thing, and in his video description, he has the complete parts list you'll need.
After 35 years, the Apple II Desktop gets an update from version 1.1 to 1.2 alpha 35. There are a host of new improvements. I installed it on my IIGS and it seems to work well. It should work on the Apple IIe, IIc, and Laser 128 machines as well.