Problem is that these cars don't have rocker arms so standard valve spring compressor tools won't work. The dealer tools are about $500. Valve stem seals aren't said to be much of a problem on diesels because there is no vacuum. Blowby is usually caused by problems with carbon build up on rings, etc.

My '87 300DT with the 3.0L version of your engine doesn't have much blowby, and my '87 190DT with 379Kmi didn't have much either. To measure blowby, I removed the breather tube from the intake and blocked it with my finger. After one minute at idle there was no noticable blowby. Now, my hard staritng '86 190D 2.5 will make enough blowby in 5-6 to cut off the motor. My project car 190DT will do the same in about 26 seconds.

How have you measured blowby?

Regards,

__________________
Brian Toscano