I have a 92 ranger 4banger and am curious what would cause an oil leak in the rubber hose that goes from the Throttle body to the valve cover. Part of my leak is in the valve cover gasket but i notice oil leaking from that hose on top of the valve cover. I am also getting a little oil in the air filter.

Any suggestions would be appreciated.

 

That hose is the air intake for the Positive Crankcase Ventilation system. My guess is that you have excessive blow-by in the engine, a bad/plugged PCV valve or a bad line in the PCV system somewhere. Have you ever checked or replaced your PCV valve?

 

I have replaced the PCV valve once. I did not inspect the hoses so there is a chance that one of them could be bad. Would a compression test rule out blow-by?

 

I'm lazy. A compression test is a lot more work than inspecting the PCV system. So, I'd check the PCV for being un-stuck, make sure that all the hoses are un-blocked, that the hose is tight on the fitting on the intake manifold, and make sure that the oil filler tightens down on the cam cover and seals properly before doing a compression test.
You should be able to run the engine with the hose from the air cleaner disconnected. The hose should develop a slight vacuum above idle speed as the PCV system pulls air through the crankcase. With the filler/hose removed, you should not see vapor coming out of the cam cover with the engine running, or at most just a tiny bit.
tom