Can someone explain the hydrostat oil change for a f935 mower, bought a $95 tech manual, just got the mower, requires 4.6 qts. , manual does not state with or without filter. I put in 5qts, no oil in site glass. do not want to overfill, please explain how the reservoir is above the site glass,but fill pt. is 1/2 the glass? Why is the transmission so hard to fill? thks.