Probably before sending the engine back, it would have been better to remove the backplate and flush the insides out with Acetone. Its
quite possible some swarf was jamming the races, or even some congealed oil. I once had a brand new ENYA 35 Special (twin ball races) which felt very rough in the bearings, but after removing the front housing and spinning the shaft in Acetone, the roughness
disappeared - just some hardened oil. BOB