any recommended rebuilt kit and manual valve body?

its very odd ran it like this for years.
after a rebuild i'm having the issue.
i hope its something stupid like a failed seal.

starting to wish i went manual (clutch peddle is still in the car)

how are 904s? i think i had one in my 2001 5.9 diesel cummins.
and i put it through hell. 600hp 1000+ torque. pulled, burnouts in 4x4 etc. put 423,000 km on it without a single issue.