Examine your diff case... and see if there is any distortion in the plastic where the spider pins slide in. If there is, you'll need to replace the diff case, and this would explain the toast spiders... if there's a change in the tolerance and one skips a tooth... that'll be the end of that diff.
I would like to know what your diff case looks like... if you don't mind examining and reporting back?
If the diff case is ok, then you could try putting Savage SS spiders in. They fit, and they've got a bit more meat on them. You can see a comparison photo of the two spiders somewhere back a page or two in this thread.