Having trouble finding source of leaks

[NB4567]

II have an 02 5.3 and I believe I have both oil and transfer case leaks and am having trouble finding the source/cause of both of them. 
The oil leak is small and I haven’t seen anything on the ground but when I checked the level on the dipstick it was low. (It was at the proper level when I last changed the oil, about 2000 miles ago). There is also oil all over the drain pan.

I’ve found small puddles of fluid on the ground and it is dripping from the bottom of the transfer case. It drips very slow, only a tiny spot on the ground about half an hour after running but overnight I put cardboard under it and there was a small puddle collected there. I haven’t had any problems driving.

[txab]

Engine oil leaks can be from:

 

Oil pressure sending unit

Crankshaft sensor above/behind the starter on passenger side

Engine oil cooler block off plate above oil filter

Last but not least, rear main seal

[richard wysong]

Common transfer case leak is the seam between the case halves. if you split the case to seal it you may find the oil pump has been damaged by the chain. they make a shield to protect it from happening again