Yeah, you don’t want to crack that plastic for sure….Maybe a razor knife gently inserted into the gasket surface? It is probably best to just replace that vernatherm while you are inside the box, make sure the check valve is clear of debris and working properly….

I got it open and all seems well. The vernatherm seems to open and close smoothly using the usual saucepan-of-boiling-water method. But of course it’s not a complete thermostat but just the thermal element. Would you still suggest replacing?

Frank pointed out a good spot for the overboard indicator tap.

That’s drilled and tapped.

I seem to remember that your control box only has a “hot light”, instead of the “hot horn”. You might consider adding the hot horn inside the box if possible. This will be very easy if your rig has dash mounted key switch and wiring.

The control box I’m using has a horn, but I haven’t tested it yet.

Once you have the gearcase off, you will probably see that the plastic water tube guides that have slid upwards on the water tubes….

Yes, they are there, I just didn’t know how to use them. I really need to get a factory manual for this motor.