FSS & non-Synthetic oil Issue

Hi, New to this Forum, not new to Mercedes-Benz

Looking for information concerning symptoms and remedies of use of conventional oils on 1998-9 vehicles with FSS. There is MB settlement of a class action suit, where MB dealers were using non-pure synthetic oils for service. Anyone have experience on this forum?

Our 1999 E300 has had a recurring symptom of having a Minimum Level Oil warning about 2500 miles after scheduled A/B Service. Minimum Oil sensor was replaced at 4200 miles, but the indicator does comes on when level is at minimum stick level. (haven't trained the spouse to check the dip-stick :? )

Only have about 25K on the vehicle, all service via MB dealers - first in VA, and now GA. During first 12K, VA dealer used Quaker State 15W40b. In 2001 moved to GA where dealer has used Synthetic only. Dealer this past week said oil use may be related to the class action suit, with remedy to open up engine which we said no.

Does anyone else have this situation?

Note: we also have a 1980 300SD TurboDiesel - that doesn't burn oil with 200K mileage, albeit we change the oil every 3000 miles, or lately at 6 months.