This is also a definite possibility.

 

Thanks for the heads up.
I spawned another thread that's on topic for that.

So, loose oil pan bolts, you say?
I think I know what caused that. I've been also trying to fix a this shaking problem my Blazer has at highway speeds. I just put new shocks on a few days ago, and I'm scheduled for new tires too. Hopefully that will resolve the shaking.

Can that lower intake manifold also spring a leak from excessive vibration?

 

I would doubt vibration could cause a leak in the lower intake manifold. If there was a leak there you'd have bigger problems with vacuum leaks and coolant leaks.

 

I went through this a few times on my old Bravada. Ended up cleaning the holes and bolts/studs with brake clean then using medium strength thread locker on them to fix it permanently.

A leaking rear main seal will coat the front of the flex plate. If there is no oil on the flex plate, then it very well could be leaking at the pan. The newer trucks have an o-ring style seal on the pan and it can be snugged up without replacing the gasket providing there isn't any junk between the pan & the block.