Three small leaks - plus other newbie questions

[hjl]

I purchased a 71 2WD Blazer last week, pictures and information are in this thread: I got one.

It's been sitting in my garage for the last four days, I didn't get a chance to pick up the plates until yesterday. I just drove it around the block a few time each day. The plan is to drive it with no major renovations. Anyway, I've noticed three small leaks. In order of worst to least:

1) Halfway back, it looks like gearbox oil leaking from where the transmission joins the driveshaft? It's (I think) the original three speed manual transmission. Is there a seal or bearing back there that can go bad?

2) A few drops of oil underneath the rear of the engine, could this be the rear main seal? I imagine fixing this is rather involved, dropping the oil pan, etc? Labor intensive? It's (I think) the original 6 cylinder engine.

3) A few drops of something oily directly under the rear axle differential, probably leaking from between the differential and the differential cover? Is this just a gasket that needs to be replaced? It looks like the original rear axle and differential, kinda rusty but not horrible.

So I've never worked on cars, and I have no wrenching skills whatsoever, but I found a local mechanic that has lots of experience with chevy trucks of this vintage. I just wanted to get the input of some board members as to potential problems and fixes for these leaks, so I understand what the guy is talking about when he tells me what it needs. I can post pictures later when I get a chance if that helps.

I'm also wondering which "must" be fixed, and which I can let slide. Despite my pathologically clean garage, the leaks don't really bother me, much.

Also, how do I check the gearbox oil?

Last question, I like reading and was wondering which manuals I can buy about this truck.