Snap quiz on fuel gauge - sensor + general question about gauges

[hippieforever3]

Since I got my bird, the fuel gauge has always indicated maximum high
(off scale). I'm not prepared to try and deal with this.

What is the best guess whether it is the gauge itself or the sensor
unit?
Where is my easiest access to the sensor?
While I'm asking ... part numbers? Can they be serviced? Repaired?
Refurbed?

I have a few other gauges that are either going to need to be replaced
or refurbished (speedo and tach). Can they be refurbed? Where?

Regards,
GPSGary
1984FC35