If the holes and the cutouts on the new gasket match the housing, why won't it work?
Looks like there may be some cracking in the housing gasket surfaces - hard to tell from the pic. The other thing to look for is warping, especially on the housing....
could be sender...could also be something has become marginal in one of the harness connections.
using the mechanical gauge would be prudent but doesn't isolate the sending unit as a potential cause of the flutter...
back a while, one used to have 5 posts before you could upload videos or images...separate forum for that.
what is your drive train composed of?
any idea whose controllers you have?
single or dual station?
Check the fitting to make sure the valve gets depressed...every once in a while I've seen it where things functioned but the gague showed a zero...and it was an interface issue.
And yes, you really need to have the boat out on the water to get a meaningful assessment...until the engine is...
what has been shown should work fine...make sure you clean up any crud where the boots seal and apply a bit of silicone dielectric grease to the boots...
Leave the recirculation hose connected ...measure the hose nipple for the raw water inlet, gat a 3" piece of reinforced hose, and then plug the open end...you can use a copper cap or a pvc cap and a clamp..
Its not the battery manufacturers, is usually the individuals rigging the boat...wings nuts are 'cheap & easy'.
How many marine batteries have you seen, with the wing nut studs, that did not have an alternative connection method ???
Not likely to find a rebuild kit.
Option one is to call the Carter's tech support line. If they can't help directly, they may be able to point you down a viable path.
Option 2 is to call Lakeland auto and marine (port clinton, OH) and see if they can help...I know they have rebuilt old...