Sounds like a hassle but I have to do similar. Not a diesel though.
Not checking the oil level and allowing the oil to be chronically low will cause ring problems as it allow the oil control rings (also called wiper rings to lose their tension or seize in the piston ring lands.
What should be done is to run both a dry and wet compression test. If there is a ring problem (and I feel there certainly is) then other than a liquid crutch such as Restore the car will need expensive engine. Additives are kind of a last gasp attempt which may work to some degree or may not work at all.