Modern Vespa

I recently reinstalled the speedo (LML/Stella) and re-hooked up the gas gauge. It's been 5 years since I had it installed, but it worked before. Now, the gas gauge needle bounces around like crazy, even at idle. It seems like the gauge is getting crazy voltage spikes and drops, though it doesn't map exactly on to engine RPMs. It does not seem to be bouncing around due to bumps in the road, but due to some sort of electrical issue.

Putting aside the general inaccuracy and overall worthlessness of gas gauges on these old scoots, I am wondering what the potential fix might be. I checked the connections to the sending unit (under the cap on the gas tank) and they are fine (clean, not reversed). I'd like to get it working again, just because...

My 2001 ET4 sat for 14 years and the gas gauge was insane after putting it back on the road in 2015...for awhile. It eventually chilled out as I rode tanks of gas through it and the sending unit worked itself up and down. Works fine now.
Only other thing to do is try to clean it (likely to be difficult and not worth the trouble)...or replace it.