Thanks for the advice everyone, I initially asked the question because I wanted to know if I was really screwing up using conventional oil. But it seems there is a lot of different choices and loyalties out there. I too am pretty loyal to my brand and since I take excellent care of my mower and change the oil & put on a new WIX filter after every mowing season ( which is about 50 hours ) I guess I'll be alright. After all, you rarely hear about an engine failure that is strictly due to a particular brand of oil. My old JD STX 38 ran and ran for 20 + years on 10-30W Valvoline.
Thanks again for the advice and input.
Thanks again for the advice and input.