[Doug in NJ]

The casings are bulletproof- it's the gear surfaces as well as the roller bearing surfaces that need to be OK. You can definitely check the front end of the input shaft (that goes into the flywheel pilot bearing). If that is beat up, it is a sign that the internals may be worn, too. If you can get the lid off, you can easily check the gear teeth for pitting or chips.

Remember, that people tend to keep the good stuff and sell the rest. So don't pay too much, hoping for the best. (That was not meant to rhyme...)

Doug