Most 8V92 coaches are supplied with Dextron ATF fluid in the PS tank. I actually use 0W30 synthetic engine oil in ours. I think you are OK with the fluid you are currently using if you have had good experience with it. Prevost has recommended a variety of fluids, as the original P/S pumps are no longer available, and the replacement runs at a higher pressure, and can sometimes produce a whine that can be heard in the coach.
Steve & Rhonda Bennett
Dana Point, CA
92 Marathon XL40
2012 Jeep Rubicon Unlimited
Owner: California Coach Company, LLC