My NSX has been out of action for about six months of this year, but on recommissioning it (with a new battery), the fuel gauge is behaving oddly.

When I fill the tank up to the brim, the fuel gauge needle doesn't seem to want to move above about 2/3rds full. I did briefly glance down on the motorway and see it indicating full, but very shortly afterwards the needle was pointing back to 1/2 full. After about 200 miles it showed a little below 1/2 full (plausible), and after a refuel to the brim again it's now currently showing just above 1/2 full. At this point I've lost faith in the gauge . . .

What's the most likely diagnosis? If it's likely to be a dodgy fuel sender I'll live with it for a bit and just refuel based on the trip meter, but if there's a possibility of electrical issues (gauge cluster caps? ) then I might have to accelerate corrective action.

Google says total failures of the sender will manifest as the gauge reading totally full or totally empty . . . are there other sender failure modes that might match the behaviour I'm seeing?