DEF gauge problem

[conantgrad83]

Looking for a little guidance or advice.... I have a 2014 I bought used 2 1/2 years ago now with 103000 miles on it.... the only problem I've had up til now is that plug under the drivers side that was coming open which now just occasionally gets wet which i pull apart and clean with electric contact cleaner and usually any CEL from it goes away (the cel I usually get is a def system problem take to dealer)... well this last time it came on i did the same routine of cleaning plugged it together and filled the def tank.... well the gauge was still reading 1/4 full... in the past I have let the def run down before filing again.... well it stayed at a quarter for a while a few threads on here had the same problem and didn't have any affect on the truck.... well the other day after a few weeks it decided to move.... down past a quarter to where the 500 mile def warning came on and has been counting down ever since..... tank was full too..... my question is should I take it to the dealer or fix it myself assuming it's the sensor ???? Get conformation from the dealer before doing anything ???? Pull it and see if I can pull out the pump and sensor and clean them ???? Problem is I'm not made of money so the dealer is go a cost me big time.... if I can pull the tank and clean it first myself i will but has anyone else tried that ???? I'm trying to figure out which way to go here.... I'm also assuming even my extended warranty is expired