Hi there,
those hydrostatic transmissions tend to destroy themselves
when they fail, the swash plate does an arduous job, changing
angle as the speed is increased to increase displacement of
the pump pistons and so increase speed, problem is a little chip
or contaminant, or overheated oil can cause the plate to 'gall'
and send metal particles through the pistons of both pump and
motor, scoring out the bores and allowing leak through. The
result is progressively less drive power, more noise and sluggish
braking. At that point parts can't fix scoring in bores, and rebuilds
never last as long as new trannies, and they must be surgically
clean at reassembly. I'd just ditch and replace. My GT2144 has a
Chinese cast iron trans with a proper spin on filter, this sold me
on the purchase, I've never trusted cheapo peerless transmissions
after my last mower, the Chinese stuff is built for global market
and appears to be properly designed for long life. Fingers crossed..