Gas tank varnish
 

Attached photo is the inside of my miata's gas tank. I can scrape the varnish off, but can't wipe it off with a rag and carb cleaner. It's entirely possible that I drove the car like this as it sat for almost four years before I got it, and there wasn't enough gas in it this time to put the varnish up that high on the tank. But I have zero experience with this. Anybody?

nvrmnd - just pulled my spare down and it looks like new inside. Would never forgive myself if I had issues down the road with this one, so looks like a swap is in order. Sure wish I'd thought about swapping the fuel pump when the rear subframe was dropped.