Virtually every oldish Merc diff has oil seeps and weeps.

But you might as well wait until they start leaving the odd spot of oil on the ground before repairing them. This can take years to progress to that stage.

Yours is a little wet and looks to be getting closer to that time. Park on a clean area after a good run that warms the diff. Check for oil spots next day.

In the old days when the Brits built motorcycles, all of them use to leak oil. It would drip from the crankcase, it would drip from the gearbox, it would drip from places where there was not supposed to be oil. If they ever stopped leaking oil we knew that there was no oil left in the system. Jaguar cars were much the same.

We thought it was normal. It was not until the Japanese starting building motorcyles that we knew any different.