I have a 90 420sel with 121k on the clock and all of a sudden I developed a rather disturbing lifter noise upon replacing plugs/wires/dist cap & rotor. I think there was a little bit of chatter all along from 100k when I bought the car to present, but now seems to be much worse. I have had the cam checked out and have a timing chain job done about 6-8 months ago. I have gone by many recommendations to go with 15w50 mobil 1 synthetic oil. That has helped the noise quite a bit, but it is still there. It seems to less noticable as you pick up speed in the car. One mechanic from the old school has advised me to drain down a little of the oil and add a bottle of Marvel Mystery oil. He said he had used it many times where lifters were noisy and in every case it stopped the noise almost completely if not completely. I have done a search and read several posts on the oil, but have not seen any on the gas engines. Can anyone give me their experiences/opinions on this and will it help. I do know eventually I will have to do some work on the lifter/rockers/cams, but unfortunately I am not ready for the repair this soon. Thanks to all who reply.