BMW Repair: 1994 318i fuel level gauge faulty?, fuel level gauge, spanner wrench

Question
Second time here and I understand that you don't go back this far on the years, but maybe you have advice.  I had the fuel filter, spark plugs and belts replaced recently and this is now the second time it has happened:  the car stopped running with just under 1/4 tank of gas.  No low fuel warning light came on.  The place I had it serviced at towed it in and said it was out of gas.  Then it happened again.  My MPG was around 26 and could get 350+ miles on one tank.  Now it's closer to 300.  Is it possible that something in the tank itself moved during the fuel filter service?  Not sure what to do as I don't want to piss off the repair shop by blaming them for this problem if it's not their fault.

Answer
Joel, fuel level snesors are notoriously crappy. You need a special spanner wrench to remove the plastic retaining nut to access the fuel level senders. I would replace both level senders. Usually the passenger side comes with the fuel pump. Get new retainer nuts if needed.
-Evan