1996 Chevrolet Blazer LX review from North America

I have had numerous problems with my 96 all wheel drive Blazer. Rear main seal replaced - still leaks, dealer now says it's the intake manifold gasket and I can't find any evidence of oil around the manifold. The only place that I can see oil is on the very bottom of the bell housing near the drain plug.

Air conditioning compressor replaced, oil lines replaced, oxygen sensor apparently bad, the garage where I bought vehicle wants to replace all three. I have been told if only the bad one is replaced, it is common for the others to go shortly after, is this true?

I recently installed a cat back system to try to increase power. Could this affect the O2 sensors?

Clicking noise coming from speedometer.

Hinge pins replaced in drivers side door.

I bought this Blazer to replace a 98 3.8L Ford Windstar (mint condition) to improve towing and found no difference in power, I've regretted it ever since.

Did I mention the bad power mirror switch? $108. I'll be rolling down the window and using my thumb!