I have a zero turn Scag STC52V-22FX with 83hrs. I want to change the hydro oil mainly because the cap came off while I mowed and I don't know if any debris got in tank. The owners manual calls for SAE 20w50 motor oil. Has Hydro-Gear BDP-10A-316 pump with Parker drive motors. I chose Shell Rotella T 10w30 Heavy Duty Conventional Motor Oil for the motor with a Wix filter but Shell Rotella doesn't make a SAE 20w50. Whats the oil to use do you think.