I was told the shop put 10-40 Pennzoil in it. When I first got it home and checked it, it was low and reading on the dipstick at the add line, so I topped it off with castrol gtx 10-40. I ran it for a few minutes, but that was really it. I am sure the engine is starting to get gunked up due to age and long periods of sitting. I have heard about chemical motor flushes... anyone have any expeirence with those products. Are they a gimmick that will do more harm that good?