I had an old 1964 Mercury Comet with a bad case of piston slap. I kept it going for another years by adding 2 quarts every 3 days of 50/50 used motor oil and 80W90 differential grease. It finally reached the point the engine would lock up after running 20 minutes and not free up until it cooled down completely. I bought a used 1978 Honda Civic station wagon with 50K on it and got $100 trade in for it. It was cheaper than paying someone to haul it off, even the junkie didn't want it!