I'll put money on the "tech" over-tightening the pinion flange nut and destroying the crush sleeve between the pinion bearings. Said "tech" probably doesn't have a clue about the inner workings of a differential and the importance of marking the pinion shaft, flange and nut before disassembly and re-installing above in the exact same position after seal replacement. Over-tightening that nut will destroy the bearings very, very quickly.
That was my exact thought. Probably didn't mark the nut before removing it and just used an impact to torque the fugger back on. If that's the case I'd push to have the diff entirely rebuilt or replaced as that'd also screw the mesh on the ring and pinion and they may be compromised as well.
