Fram PH7575 is what I use on my STX38.
how do i check the hydro transmisson fluid on a stx38
30 lbs
On the deck
stx 38 fly wheel
I can not find one either
Go to http://outdoorpowerinfo.com/repairs/deere_stx38_gear_drive_belt.asp for pictures and descriptions of installation of drive belt and deck belt for John Deere STX38 Tractor with black mower deck.
bladebelt diagram for john deere stx38 yellow deck
Outdoor Power Equipment Website
moostxc255457
There should be a tag on the very rear of the mower, behind and below where the drivers seat is that will have that information. what years were john deere 920 built
Check your idlers on the deck as they are the most common culprit.