A "wet" compression test is another good data point - squirt a little oil in each cylinder and run the compression test. If the values are much higher, it indicates that your rings are worn.
A leak down test is done with a leak down tester and a supply of compressed air. Basically, air supplied at a known pressure is provided to the cylinder via the spark plug hole at TDC (this must be pretty accurately determined or the air pressure will turn the motor) of the compression stroke (both valves are closed). A gauge reads the air pressure in the cylinder. If percentage of the pressure lost in the cylinder (the difference between the known input pressure and the pressure in the cylinder) to the supplied pressure is more than, say, 20% - the lower the better - you might have a problem. You can tell where the air is leaking by listening at the exhaust, intake, the intake and exhaust of the neighboring cylinder, and crank case breather.
A good shop will have a leak down tester or you can get them from Amazon, ebay, or a discount tool place like Harbor Freight for about somewhere in the neighborhood of $50. Joining a local sports car club (MG, Lotus, Triumph, Canadian Automobile Sports Car Club etc.) is a good idea not only for the camaraderie but to have access to people who are more knowledgeable (and with a bigger collection of tools!) than you. Quite often they will have a collection of tools for their members and often a leak down tester is one of them.
