My motor coach hydraulic system calls for Dexron III. The hydraulic system runs both the power steering and the side radiator fan. I want to drain out four gallons of the old Dexron III and replace the filters. Can I mix 4 gallons of Dexron VI with the remaining 7 gallons of Dexron III that will still be in the system? I read somewhere that Dexron VI is not compatible with Viton seals. I don't know if the hydraulic system has any Viton seals or not, but I don't want to cause any damage. Or, I have several gallons of BP Autran Sun 295. Would it be better to mix that with the old Dexron III? Confused.