From what you have told us I really can't point the finger at any particular culprit. Look at the recent history.
The gearbox has done 40000 miles and has not been overhauled. It can not possibly be in mint condition at that mileage.
The DMF is now very secondhand, even if it was renewed 25000 miles ago.
The clutch is new yet it appears to be slipping. It should not be warped or significantly worn under normal driving conditions, but can easily suffer those faults if maltreated by harsh driving for as little as 20000 miles.
For the bearings to fail in the previous gearbox is unheard of in my experience, which suggests it had a very hard life. That in turn also suggests the whole transmission had been equally overloaded. All I can suggest is to remove the gearbox, clutch and DMF and thoroughly inspect and, if necessary, overhaul them.