I do remember having to change a gearbox casing on one though. IN reverse, if you dropped the clutch with a bang, and they hadn't bothered to fit the locking washer, the big nut on the layshaft would spin off the shaft and mill its way through the gearbox casing..
I vividly remember borrowing a socket and LONG torque wrench and fitting scaffold pipe over it to get the new nut back on at the most torque -
150in lb- that I have ever done a nut up to. And then banging the new lock washer (there wasn't an old one of course) back to lock the nut...before refitting the new casing, bearing and seal..