Selene,
Interesting issue regarding the bezel on your gauge. I'm NOT by know means an expert, but it looks like some water contamination made whatever some ferrous material (needle/springs/armatures??) rust. At least that's my first impression by looking at the photo.
So I'm not sure if it's feasible, much less warranted to just replace the bezel as opposed to replacing the gauge itself or even the whole unit. Which of course brings up its own set of issues or possiblities:
1-Gauge Replacement, OEM or Aftermarket? Who Manufactures or sells these things?
Moeller Marine has complete Direct sight units, though you have to determine which size you need. They have just the Replacement Direct Site Gauge as well, but will it fit the unit that's installed? Maybe it's all universal, I haven't a clue. I've always been bitten by Murphy's Law in these situations, that's why I learned to keep careful records of Manufacturer's, Part No's, and even Vendors of what I purchase!
2: Replacement issues. Gas operated A4 owners such a myself have a bit more of a safety concern than diesel owners. As an A4 owner I myself would find it worth seeking professional help, at least getting a quote. I'm sure it's easy enough to follow all the safety precautions, but then again is it worth my time ($$) to do it myself? Just a thought and quotes are usually free.
3: My Gauge isn't corroded like yours, and I do like the reliability of the mechanical gauge, but if it was and I was going to replace it, I would consider going with an electrical sending unit , such as a Moeller Reed Sending unit and electrical gauge mounted somewhere convenient in the cockpit. They're easy to install and you only need to know the depth of your tank. FWIW, on my previous boat, I had two (port/stbd) 12 Gal plastic Tempo Tanks installed in lockers which made reading the mechanical gauge a hassle. So I purchased and installed the straight "Reed Switch Sending Units" in each and ended up wiring them to a CAN Bus where I could read the fuel level as well as consumption rate on my GARMIN 540s. It was a sweet setup lol. It was real easy to do, but since the TEMPO's were portable, I easily removed them, drained them by filling my car (bonus!), and let them air dry until the fumes were gone before commencing work. That's my one real worry should I have to do something on the Pearson. Drain and wait I suppose. It's not the gas itself that bothers me, just the Stoichiometric Air-Fuel Ratio of an empty tank!
My port on the cockpit deck is cloudy as well. I'm looking to see if I can get an appropriate size disc of Gorilla or Dragontail glass to replace it. I'm also thinking of possibly removing it altogether and replacing it with a similar sized Screw Out Deck Plate / Inspection Port. Just a twist and I see it clear as day!
Finally, I record my fuel usage as well. But I'm curious how others do it. My gauge is divided down to 16ths. So what do makes sense to record in? Percentage? 16th's? 8th's? Quarters?? Or convert to gallons like 9/16 = 16.88 gallons in my case. Or record as 68%? Or even just round down to 1/2? I suppose that's a matter of preference. FWIW, I convert to gallons for the record as it's easier for me as a unit to work with.
Just some thinking out loud lol!
"Sub" Ed