Try the checkvalve
I had a similar issue in that the sump pump would run, but could not empty the sump basin. Downstream there is a check valve to prevent gray water from flowing back into the sump. It had ‘frozen’ and would not let water pass. In my case I bypassed the check valve with anew...
Installed Vesper xb-8000 last summer. Displays the targets on my iPad wirelessly in both AquaMaps and Navionics (as well as its own app). No need to complicate the install by interfacing to existing proprietary MFD.
I went through this last year and landed on a GoPro broadcasting to my Ipad. Its wireless (bluetooth), does not require wiring for power (both have batteries), and you can record for post docking review. Also, I already owned both, so cost = $0.
Having similar requirements, we bought a Portland Pudgy. She can be a life raft, she sails, rows well and can handle a small motor. We mounted an ePropulsion Spirit electric motor which works great.
Did you find a solution?
Kevin,
We just bought an OA 423, coincidentally in Essex, CT at EBW. The screw trim is as you described in your post. Did you find a source for replacement?
Thanks!
Marty