Leaking oil removes what is ever typically in the oil as well as the oil. Burning oil typically removes the lighter components of the oil mix, leaves the soot in the sump. Adding make up only dilutes it a little & gets the concentration of soot etc back close to the pre burn level.
The oil in an oil burner decomposes quicker as the combustion products from the oil burning partly go into the oil.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving