I did find the valve: it’s starboard aft hatch tied into the old bait well pump (no baitwell on the boat) I followed the clear hose and it led to the raw water pump. the discharge side of that hose ran off into the port side and I believe the other end is that frozen valve you suspected. I disconnected the discharge side and added a hose right at the pump; works for now. I’ll need to work onn getting the seized valve replaced. Thanks for your input!