Your best bet would be to clean off all the accumulation of old fluid first.
Then check it for leaks. Both the power steering lines sit on top of the box, one of them leaking could give the same indications.
And yes it if is the seal on the input side it can be replaced, not a normal DIY job.
And I'd look for a used box before spending that much on a new one.
97 Sahara, 74 Renegade, 72 CJ5, 55 Willy's (the Beast) Boss 302, 6:34 gearing, Bose 901 speakers.
God I miss that Jeep. Forgot the kinda Jeep, 80 SX4.