Bands can be adjusted with just dropping the pan. But replacement I think will require removing the unit and pulling the pump.
But since it wasn't sudden, maybe its an adjustment. Also I'm not clear on whether 2nd and drive are working. It is a full manual VB if I understand correctly. TA will know their valve body so probably can be more helpful. I'm not a transmission guy at all. Just rebuilt my own once. TA was supplying MP for years so other people will also know.