A hammer was not used, just my seperating tool that I made based on the one in the workshop manual - I really thought that it was going to break before the cases seperated !
Depite the case being too hot to touch (used my leather gardening gloves to handle the case) the bearings remained in the cases when the cases seperated.
I would have thought that the bearings would have came out of the cases given that the expansion rate of aluminium is greater than that of steel, so does make me wonder if the same idiot that used loctite on the gearbox sprocket nut has used bearing lock on the bearings.
Looking at the joint faces there is no sign of any sealant but plenty of evidence of oil between the mating faces so I hope I have found the source of the problem.
Wellseal is my jointing compound of choice so the joint faces will be treated to a coating of that prior to re assembly.
I just hope this is all worth it.