Your trans temp light comes on at 140 C. That's very hot for normal ATF. If you believe heat damaged the seal in the oil pump, imagine what it would have done to the thinner seals on your clutch pistons.
IMO, it's harder to remove and refit the trans than it is to pull off the bellhousing and valve body to pull just the reverse & high clutches to see what condition they're in.
An internal seal, o'rings and friction set is about 1/3 the cost of a Nomad valve body.
Seriously, if you have heat related damage then you'll only be throwing money away fitting a Nomad without opening the trans..