Essentially if your Engine runs the Car OK blow-by is only a nuisance.

I believe there is only 2 fixes depending on the cause.

If Piston Rings are sticking there is some possibility that instilling something like Marvel Mystery Oil (or something else) into the Cylinders and letting it work for a week or 2 might free up the Piston Rings.

If it is cylinder, piston ring and piston wear is the cause then the fix is to overhaul that area.

I believe a few have reduced blow-by by replacing the Valve Stem Seals but most including myself did not have that happen

The nuisance issue can be mitigated by piping the blow-by someplace other then inside of the Air Filter Housing; at least that is what I did on mine.

__________________
84 300D, 82 Volvo 244Gl Diesel