I'm going for glazed kevlar lining myself.
It's unlikely that a New T/O bearing would leak causing fluid to get on it but it is still possible.
Bad random thoughts...
Rear main leak.
T/O bearing leak.
Water/heavy rain contamination.
T/O bearing dust cover/inspection boot missing, removed, or etc.
Spilled fluid. Highly unlikely as it's sealed well, but you had mentioned the tranny was just serviced?
