what is the most common failure of a rear diff?

is it because of the casting flexing?

reason i ask is because i was sold a 4x4 rear beam and diff as a 2wd item (didnt know any better at the time as it had the 3dr swingarms and rear arb...)

anyway, i am hoping for around 400ish bhp when the 3dr is up and running so thinking about getting a strengthening plate made up.

or failing that, i have a spare diff that i will get welded lol