I'm not sure what the deal is with the Mobile oil and this engine, I have never used it but it does appear that they don't work and play well with each other. I know other people that use Mobile 1 synthetic oil in other engines without any problems. There are many good quality oils and I will not debate which one is best but I will tell you what I use. I use Penzoil for Air cooled engines at 32:1 for the first 5 gallons. Then I go to Stihl HP Ultra synthetic at 50:1, engines run like mad and are clean as a whistle. I still have one of the first generation DL 50's, over three years old, it runs like a scalded ape and aside from mufflers, it has given me no troubles.