I just purchased a 1990 E300 (2.6L) with a M103 engine with 176K miles and I noticed that the car runs rough especially when I put it into gear. I did a leak down test and it seems that cylinder #6 has low compression. The car does burn oil but does not smoke. Could this be a burnt valve problem or is it just the valve seals that need to be replaced? Can this problem be fixed without removing the head? If not, is the head removal pretty straight forward. Any special tools needed? I am trying to decide whether to keep the car or sell it. Any help is greatly appreciated. Thanks.