Keith, have you looked into other things like properly working ignition components? A poorly firing ignition system will foul plugs fast. Is the carburetor setup properly? Has it been rebuilt? Are you consuming oil at a fast rate? If so, I would suspect bad rings before any vacuum leaks sucking oil. The only place oil could get to the combustion chambers, is if the head gasket was leaking, or the rings are worn, or as previously stated - the valve seals are bad. Valve seal problems are typically only a problem at startup, where you will see a puff of smoke when the oil burns off inside the combustion chamber. Drivability should not be effected, unless the seals are reallllllly bad.