It's not a huge deal to pull the entire gas gauge assembly - you can do it without removing the instrument panel, but it's easier if you do. I'd suggest that you get a "gas gauge rebuild kit" and a set of the special wrenches from the vendors. Be sure to get the fuel level in your tank well down before you do. Most of the Model A maintenance or restoration books have the procedure, but if you're at all mechanically inclined it's pretty intuitive.
Most gauges that have been in for a while have hardened gaskets anyhow and leak vapor a bit so it's good to refresh the gaskets.
JayJay