There is a spacer, referred to as a distance piece, that slides onto the axle stub and contacts the inner races of both the inner and outer wheel bearings. It is fitted with shims of different thicknesses to result in the proper preload on the two bearings. It may be that there are too few shims on one side. That is assuming there is no other issue such as pitted or somehow damaged bearings on that side. The procedure is outlined in the workshop manual but I'm sure if you do a search here you'll find a thread on the process. The distance piece is sometimes not installed, whether out of ignorance or believing it isn't needed. Austensibly it makes the axle stub more resistant to stress but the presence or absence of the parts can't be known unless you disassemble the hub. I drove my late model BN2 without them for a while before I bought the parts and set it up properly.