Just purchased with 143k on it. Being a sludge engine I was going to RX it but I put on 2k miles with a change of QS 10w30 dino. The oil seems clean and has burned approximately 1/8 of a quart. The oil filler in the valve cover was black and the cap was also black with a little build up. The engine and trans have zero leaks and runs like a Singer sewing machine. Should I RX or go PP.