I have a John Deere 757 zero turn mower that calls for 15w40 in the drive system. It calls out Plus-50 specifically in the manual. I have used 15w40 Rotella in the past and Schaeffer 15w40 in the engine. Would anyone have a preference or any advice in selecting an oil for this system? My two easiest options right now are: 1. stick with Rotella or 2. run the same Schaeffer product that I use in the engine.