In my case it's the 20yr old Briggs VanGuard 16HP on a Simplicity Tractor. About 600 hrs. Used Optimol Conventional 30wt first 2 years. Then M-1 15W-50 Redcap and Goldcap Now Motul 300V Diester 15W-50 B&S oil filters now M-1 Had a few Blackstone samples done and they showed usually 2-3 ppm iron everything else was clean. Engine runs better than new!! How about you folks? What engines? Applications? Hours? Oil used? How often changed? Oil filter; what brand?