@nsPerFoot
Assuming there really was a file named gupdate.gcd in the Garmin folder before you used the SD card, it seems to have been deleted according to the update.log file. However, my strong suspicion is that the device's internal regions can only be read but not written to. That's backed up by your unsuccessful experience trying to flash Cure3 firmware which is intended to be written to region 14. QuickCure on the other hand is universal and is not firmware dependent, in fact it doesn't involve a device's firmware in any way at all. Similarly, the attempt to flash the 14.bin and 127.bin failed.

I think almost certainly that you're correct, it has a failing flash chip and it will eventually die completely. As you're likely already aware, it's exhibiting much the same symptoms that a bad media card does, i.e. it doesn't save files written to it and deleted files simply re-appear.

@Zakk
Unfortunately it seems your nuvi 30's flash chip is also failing, it just has somewhat different symptoms from those of the previous poster's.