I have a Jeep Cherokee with the 4 liter engine. It's got 98,000 miles on it, and I'm sure the insides are pretty dirty as the previous owner rarely changed the oil. I cleaned off some pretty big chunks from the inside of the oil filler cap. It's got a stuck lifter, or something in the area of the valves making a tapping noise. I was thinking of running a quart of ATF in the crankcase for a little while at idle to try and clean it out/stop the tapping. Might this be a bad idea? I mean, I know you're not suppost to switch to synthetic oil on a high mileage engine, because it can start to leak. Wouldn't this be kind of the same thing?