'87 Volvo 740 Turbo - 320,000 miles. While I am waiting for my front wheel bearings to arrive, I thought I check the compression on the my engine.
I did the "dry" and "wet" compression test, but the pressure gauge went down to nearly 0 immediately after I stopped cranking the engine (I assume that the borrowed compression gauge is not the best) Anyway, here is the result and I need your input what you think it is or how I could do some more checks to verify if its the piston ring or something wrong with the valve:

Cylinder dry wet
#1 180 185 (front)
#2 170 175
#3 175 185
#4 80 80 (fire wall)

that's quite a significant low pressure in cylinder #4 - I don't see any smoke coming out of the exhaust (at least not visible)
the spark plug looked pretty normal

engine is quite oily on the outside - first I thought its due to the oil separator being plugged, but I checked that one. So I am not really sure where the oil comes from.
it looks like the is quite a bit of oil coming from the crank case to the inlet, but not sure.

Any ideas - slowly I am getting tired, but since I LOVE wagons with rear wheel drive and manual transmission I don't think I have much of an option than to keep him alive ;-)

Since it is such a big difference, I don't think it can be the valve guides, so I am thinking bad valve, or broken valve spring?? Is that possible??