Question on differentials

Hello

I have a different question about the drive/difference.
What are the most common sufferings and how do they express themselves?
What do I have to pay special attention to and what does it mean to me sooner or later?
Which maintenances are to be made/which oils and how or what is best to do or how can it be done best?

That makes me feel a little bit better at the moment, because I haven't touched it yet, but I don't want to start when it's already too late at the end.
I'd be happy about every good tip.

MFG Weasel