Hmmm, so it seems like "printenv" shows the environment variables, "setenv" is used for setting them, and "saveenv" (hopefully) saves them to flash. It doesn't seem to list an explicit way to delete them, which might mean that "saveenv" with no value might do that. Or using the "=" sign, as you mentioned in a post too.
If you create a brand new environment variable and save it, is it still there after you reboot the switch? Also, how to embed spaces in the value?
Something like:
=> setenv mytestvarA 123
=> setenv mytestvarB '123'
=> setenv mytestvarC "123"
=> setenv mytestvarD "123 456"
=> saveenv
Then reboot the switch and see if any of the "mytestvar*" variables show up with printenv.
With the corrupted 9024D-M, I'm not sure which environment variables need to be set. Experiment time.
(note - edited for typo fixes)