Compression Test on W124 '90 300E

[AndreiFS]

Hello,

I have a 300E with 110,000 miles on it. I get grey smoke from the exhaust between idle and 2500 RPM. I read that this could be valve seals. I did a compression test and each cylinder did the exact same thing. I did three strokes of the engine and the readings (in Bar) were: 9-10-13 on all cylinders. I understand that 8.5 is minimum for these engines. According to Haynes if a reading starts low and then jumps the rings are suspect. But would there be such a coincidence that all six pistons have worn rings? So far, does it look like the valve seals could be problematic? And finally, approximately how much is a stem seal job?

Thanks, Andrei