Do a search. You'll find lots of threads on this topic. There is a great deal of reported differences in blowby on otherwise healthy engines. One test that is suggested is to block the breather tube and count the number of seconds before the engine shuts down. The longer the time the better. I do not recommend this because it puts a lot of pressure on the seals.
I suggested at one time that we all agree to use a standard 40 gallon trash bag, attach it to the breather tube and measure how long it takes to inflate. That'e the only objective test I have been able to imagine.
A general consensus seems to be that as long as the engine has power and starts well when cold, the amount of blow by is largely irrelevant.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13