I have a 1980 350 block that was claimed to be rebuilt when I bought a 67 Camaro last winter. It's using oil in as little as 100 miles, about a half quart, barely visible smoke on deaccelration, but oil fouling the plugs bad. Ran compression test and got 180 to 200 on all cylinders. Put oil in the cylinders and reading stayed the same. Is this a sure sign of bad valve seals or valve guides? Is this a positive indication of bad valves? or could the rings be bad too? This motor runs strong! I was surprised how fouled the plugs were, only knew they were fouled because I pulled one out, it did not affect the performance of the car. Any suggestions would be greatly appreciated.