I'm looking to put the best gear oil I can in my land pride 5615 rotary cutter gearboxes. The manual doesn't state anything special besides 80w-90 with EP additive. I do actually run the machine about 630 pto rpm instead of the typical 540 rpm. It cuts alot better in vibrates alot less. I figure in the 110 degree Texas heat that may add some extra heat to the gearboxes from the over speed. I'm thinking about using either a SAE j2360 mil spec oil or either the Motul gear 300 which is a very expensive ester oil. I see nothing but rave reviews about the motul pro gear.