My X300 was running fine for most of the day and then it just lost power and quit. I thought I was out of gas, but the tank was almost full. I replaced the fuel filter and while I was at it, checked to make sure that the fuel pump was sucking (which it was) when I cranked the engine. I then used LP air to blow into the fuel line see if there was a blockage between the fuel filter and the tank. I forgot to take off the gas cap before I did that and it popped the vent hose off. It was a pain to get it back on, but that proved that the fuel line wasn't blocked. After scratching my head a while, I tried that again with very low pressure to see if I could hear air bubbles in the fuel tank and instead, I heard a hissing sound that made me think that the fuel pickup was no longer connected inside the tank. At the local JD Dealer, one of the technicians said that on older tractors, it's not uncommon to have a fuel line get soft with age and collapse. You can still blow air through it, but you can't suck fuel through it. I'm going to replace the fuel line today and if that doesn't work, I'll try to remove the fuel pickup and see if I can find a problem. Fortunately, I have a borescope, so maybe I can look around for debris in the tank. This is very baffling.