Synthetic oil use on flat tappet cam after break in

over 15.000 miles combined on a 340 and 360 stroker using synthetic Valvoline vr-1 10-30 racing oil or royal purple 10-40 xpr after breaking in with dino oil. Over 12 years on the 340 3 on the stroker , no problems yet . 340 was a flat tappet ., never burn oil between changes every 3 or 4 thousand miles , never had a leak either. synthetic works for me . but that is just me , maybe i'm lucky