Need help with fuel gauge not working?

I recently had some work done on my 74 Duster at a local shop, as he replaced the wiper linkage bushings and installed the Schumacker pivot seal kit. Prior to this the fuel gauge worked and now it reads E and there is about 10 gallons of gas in the tank. The mechanic said he checked the wiring and all seemed in good order, and he thinks the float cracked and filled with fluid and sits at the bottom of the tank, thus the reading of E.

Your thoughts and opinions? Any way I could verify his findings, before I pull the tank and replace damaged parts?

Thanks Gary