malrnod

I have the Regent model with 14 HP Vanguard engine. I think it's about 11 years old. Recently, the forward maximum speed has been reduced from what it used to be. I don't know how to add transmission fluid and don't know the exact type of fluid to use. There's a filler tube with a cap just under the seat and battery compartment.
I don't know how to determine if the hydrostatic transmission is filled correctly either.

Any suggestions would be greatly appreciated. There is no information about this in the operations manual for this Regent model no. 1692354