Your lab results show "insolubles" as 0.3%. If they mean soot, then you could safely use a much longer OCI without risking exceeding the soot load limit of 2%.

You could pay extra to have the TBN sampled, which would be another possible limiting factor. I think when the TBN goes below 7 or 8, assuming it started at 11 or 12, then you need to change the oil. Haven't studied that for years. Next limiting factor is oil viscosity.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC