I hate it when people tell you to add a little bit of oil to check if your rings are bad. Um, if you add a little bit of oil to a motor with perfect compression, guess what, the compression still rises. So, are the rings bad on a perfect motor? No, the oil itself just adds slight compression and increase the seal of the perfectly good rings.

The only thing you can do is a leakdown test and that will only tell you if you have an excessive leak. The only true way to know if your rings, or valves or whatever it may be are bad is to open up the motor.