Update: BMW replaced the differential as per PUMA 44236082 yesterday. Parts list:

Qty. FP number. Description
1 31-50-7-544-478 Puma Info Case Requ
10. 83-22-9-415-960 1/10 liter final drive
-1. 31-50-7-544-478 Core return

Description of cause: frt diff leaking from case halves. Needs frt diff. Need Puma case for replacing of frt diff.

It is cold-ish again this morning (-17C) so one more day to see if anything happens then it looks like spring is arriving in YYC so won't really know if this is permanent until November.