Yep, sorry to say... it's time to pull the trans for overhaul.
Edit; there is still a chance that the broken snap ring jamming the valve also prevents the band from applying in manual second.
Might be worth pulling the VB anyway for a look.... before yanking the trans out.
I just checked the hydraulic circuit diagram... and IF the OD regulator valve is jammed from the broken snap ring... it will also cause the band to NOT apply in manual 2nd.
Advice... pull the VB first.