Try putting some oil in that number 5 cylinder. If the compression readings come up, say from 50 to 115-120, then it's worn out rings. If it doesn't come up, try that air pressure test I mentioned. And if you don't have a compressor, pull that cylinder head and inspect the valves and piston. With the head removed, fill the intake and exhaust runners with water and see if the valves for that cylinder are leaking.
Edit: our posts crossed so some of this is redundant
1973 VW Karmann-Ghia first car
2009 Challenger R/T 6MT, Flowmaster, inTune daily driver
1977 CJ5 304, 3MT - under construction
And many in between!