You can test the efficiency of the rings by doing a simple wet / dry compression test.
Remove all the spark plugs and the fuel pump fuse, relieve the fuel system pressure and do a dry compression test in all the cylinders. Record the numbers. They should all be roughly the same, within 10 % of each other. If one is significantly different from the others, then that cylinder is leaking.
To determine if the RINGS are leaking:
Go back and do the compression test again, but this time put 2-3cc of engine oil in the spark plug hole first. Record the numbers. If there are bad rings, the pressure will be significantly higher for the wet test since the oil seals the leak past the rings temporarily.
Let us know what you find.
I'd say that if the rings were bad enough to be causing a misfire, it would have been visible as scoring on the cylinder walls, and he should have notified you of this before continuing after the cylinder head was removed. Either he's wrong about the rings and something else is causing the misfire, or he missed the diagnosis, plain and simple.
Last edited by windsmith; 12-13-2011 at 05:09 AM.