So, a C172 I sometimes rent, G1000, had the right fuel gauge showing a big red 'x' last time I went to fly it a couple months back. Quick check of the 'required equipment' list confirms that even for day VFR, both L and R fuel gauges must be working, so I scrubbed that flight and made a note to the FBO manager and on the dispatch squawk sheet. Fast forward to today, 2 months later. Booked the same plane for some lunch T&Gs. I always go out to the plane first thing when I get there to click the power on and check fuel levels, so I can accurately compute W&B and determine if I need to take on fuel before departure. Well, dang if the right fuel gauge isn't still showing a big red 'x'! The guy behind the counter expressed surprise when I told him it wasn't working (again), stating that it worked earlier in the week. I said that with the gauges being required for Day VFR, I wouldn't take the plane, even for pattern work. A short conversation ensued where he tried to persuade me, gently, to take the plane, as the gauge worked 'sometimes' and was being 'intermittent' and they were trying to chase down the root cause, perhaps a "short". "Short? Near fuel?!" says I. "No thanks." "Well, the wires on the gauges and floats are all encased, not exposed." I explained that they are SUPPOSED to be encased, not exposed, but since they hadn't yet tracked down the root cause of the "intermittent short", who knows?! I didn't want to lose a wing in an explosion on downwind, and declined to fly the plane, and took a round gauge 172 instead. Had a pleasant flight. What about you? Would you have taken it? Am I being overly cautious? I don't think I am... the rules are there for a reason.