i'm looking at one 85 gsl who's gas gauge is broken. how hard is the tank sensor to replace?

 

To replace the sensor ya gotta drop the tank. It's not hard just time consuming. Your sensor, however might not be bad. There's a connector that attaches to the outside of the tank and it's right behind the left rear wheel. I've seen dirt and road crap get piled on top of that connector causing the contacts to corrode. Sometimes just cleaning those contracts up will solve the problem.