Engines wear out everywhere at the same time. You should see a slight increase in compression when adding a squirt of oil. It's sealing the wear in that cylinder. It sounds like a valve problem if you don't see a sizable increase. toolman
With the above said, you squirt the tablespoon of oil (SAE 30W is fine) into a cylinder that is reading low. Crank the engine two revolutions or so to spread the oil then retest the cylinder. If the compression comes up markedly, 40 PSI or more, the trouble is poor ring to bore sealing. If compression doesn't increase much, about 5 PSI, then the problem is probably with the valves. It could also be pulled head studs or a warped cylinder head.