Toyota Repair: 91 toy oil burner, worn piston rings, valve seals

Question
91 camry 170,000 miles, is burning oil, I can smell it
however no leaks anywhere visible. No loss of engine performance and no engine lights on.
what could it be and at what cost? Is it worth fixing?

Answer
A common problem is that the valve seals are leaking, if there is blue smoke from the tailpipe when the engine is first started but then disapears then this is the case and the vale seals should be replaced, if the smoke is there all the time then the problem may be more serious such as worn piston rings.