By roller I assume you mean ball shape bearings?
That said I assume then it doesn't matter which way it is installed as in no front or back to it?
The metal shim you mentioned i assume is between the drum backing plate and the axle flange?
Doesn't the 4 bolt bearing retaining plate use some sort of gasket as well? I thought I saw something when I removed it like a paper gasket type?
Maybe someone used some RTV under the cover?
I hate to ask about oven temp and time in oven?