You essentially said they were running well. That usually means leave things alone.

The IPs need occasional re-timing. I can't give you a mileage on that.

On Fuel Injection Pumps that use Vacuum the Diaphragm gets old and less flexible and the housings that the rather small Shafts go through wear and or need new O-rings. There is a test for leaks in the Service Manual and on this forum.

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84 300D, 82 Volvo 244Gl Diesel