I recently bought a WELTMEISTER TO 10 (German Democratic Republic) which was a real mess. Keys totally bent, fuse gone, fuse lid gone, interior parts missing all the way.
First thing i wanted to fix were the keys. They could be pressed but came up way too high. Unscrewing the case showed that this was an easy fix: All the faulty keys had their ends (which hold them down) badly bent. At first i tried un-screwing every key and then re-bnding it, but that's too tricky. Found an easier way: Just pull the bad key waaaay up. The bent end should be visible now. Take a big screwdriver or something similar to re-bend the ends of the keys. Bend them over the top, so the key can slide back into its place properly. Now take a look at the whole thing from downside: The end is overbent. But that's no problem, just bend it into place, like you can see in the pick.
Missing key contact wires:
I already wanted to trash the whole thing when i saw that like 15 key contact wires were missing. But sometimes you just get lucky: When shaking the organ, nearly all the missing parts (ca. 30) came tumbling out. What a surprise! Among them were most of the wires! Yippee!
Check the pic to see the missing wires from the downside.
Replacing those bastards can be a little tricky. Have two screwdrivers ready. The pic should give you an idea how they should be placed.