91 Ls400 Fuel Gauge Stops At 3/4

[rct20]

My 91 LS400 dashboard fuel gauge tops out at 3/4 full even when the tank is full. The dealer said it is shot and needs replacement for some ungodly amount, $750-1200 if I remember correctly. Is this something I can replace myself and if so, how difficult and involved is the process? Where would I get a replacement part. I have never done any work on the car myself before and I don't want to mess this up. I can live with it, and have for 3 years, it's just a little annoying and wondered if I could fix it easily myself.