I have a 91 Chev pickup with the 6.2 diesel. It runs very good & smooth but it is consuming/burning vast quantities of oil (one quart per 75 miles). It does not leak oil (that I can see). I get lots of blue smoke when the engine is under heavy load (up steep hills). Is this a new engine situation or a ring/valve job? What is a fair price for a ring/valve job?