If there is an access hatch over your fuel level sending unit, you can open that up and look inside the tank to get a visual of any issues in there. I would start with that. Be careful with the loosening and tightening the screws as the aluminum is pretty soft. Also would be good to have a replacement gasket on hand to get it sealed back after removing.
If the fuel is dirty you can look into a fuel polishing service that cycles the fuel through filters then puts it back in the tank. If the tank is the issue, then hopefully it's just ethanol varnish you need to deal with.
You can also see if your tank has a label in that area so you can identify the manufacturer and serial number. You'll want that if you start going down the road of tank replacement. It's definitely old enough that replacement might be necessary, but plenty of people get a longer life out of their tanks if they've been lucky enough to avoid moisture settling around the tank cavity to induce corrosion and leaks.
While you're messing with tank related work, you might also have someone do a low pressure (~3lbs) test of the tank after remounting the sending unit just to be sure you're not showing any leakage. If you can pass that test there's not much reason to replace the tank today.