I have 3 leaks, any idea on how serious these are?

[Rui]

97 A6q wgn, 38K.

Recently had my car in for a checkup and my tech showed me three leaks as follows:

1.Right rear differential axle seal leak (mild, no dripping, just moist on the outside)
2.Transmission shaft seal leak (no dripping on ground but slight dripping onto the hot cat which
results in unpleasant smell)
3.Crank sensor leak (mild, no dripping, just moist on the outside)

My tech recommended I do them reasonably soon, especially the transmission one.

Has anyone come across these? How worried should I be? Should I just go ahead and have them
all done? And any ideas on what this could cost me?

Thanks in advance for any replies!

Rui