What is an acceptable difference between a dry and wet compression test that would not indicate pressure lost past rings? I have heard that 10% is normal and I have heard that there should be no difference at all if rings are ok.

 

Any time you put more than a couple of CC's of oil into the combustion space, you're gonna get a change in compression numbers regardless of engine condition.

A leakdown test is a far better indicator of cylinder condition issues

 

A 10% difference between dry and wet test is normal in many systems, especially if the rings are in good condition and there are no visible leaks.