My 372 has the rubber cap for filling purposes.
The level hole is I belive on the L/H side, it is a bolt head @ halfway up the side of the tranny.
I had a stuck 3pt once on the 372, the tractor had sat for a good while and the piston stuck (for whatever reason) so all I did was put the bush hog on it and jump up and down on the bush hog till it broke free. It has worked fine since and that was @ 5 years ago.