Hard to say without seeing/hearing it. The description sounds more like an axle problem. Clunking differentials don't " floored car from stop thru all gears " and then drive away.
An axle that klunks is harder to prove (if its not obvious) than the differential. With the diff the cover can be removed and everything is easily exposed.
Used differentials should be plentiful and cheap. (and a pretty good value as they do last a long time - usually)
Bosch Master, ASE Master, L1
33 years MB technician