Pressurize a cylinder that is at TDC, compression and listen for air leakage in the dipstick tube with a stethoscope to identify ring leakage. Listen in the tail pipe for exhaust valve leakage and in the airbox for intake valve leakage. Valve seal leakage is harder to identify but it is less of a concern.
76 Suzuki GT500
2011 Jaguar XKR
A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke