mine used to flicker on and off, now it just stays at full. im positive it is not the fuel level sender because my light still comes on when the tank is empty (i commute a lot and measure mileage). ive taken the cluster apart quite a few times already, and havent seen any loose or corroded parts, but i can check again soon. also, we have the newer si boards and our batteries are lithium, but i know they still go out.. my si lights stay red lol even after reseting it multiple times..
oh yea and that smacking the dash thing works, sometimes. my gauge cluster just sucks =/