T680 fuel pressure loss mystery

I'll try to make this quick and easy. During pretrip yesterday I twisted off the cap on top of the fuel water separator. I don't have an explanation for doing it other than being like a kid in a store wanting to touch everything. I tightened the cap back till it clicked and finished PT and drove 20 mins-shut the truck off- came back after twenty mins and truck wouldn't crank. I tried 4 or 5 times with no luck-started looking around on internet and whatever else my non mechanic brain told me to do(never opened the hood). Finally I hear a voice in my head saying give it another try for a bit longer. I do- and then I hear it trying a little better and then finally it goes. So after this I drive 400 miles, stopping here and there but never turning off truck. So now I'm at a shipper and I'm backed into the dock and I decide to turn her off. It was the fastest load ever. I don't know if it was even 20 minutes that went by. Try to crank up and leave and not turning over. I do open hood this time and the water separator is showing zero diesel -dry. I take off top cap and the o-ring falls down quickly and easily. It seems unlikely but could i have not seated the o ring well earlier that morning? Fast forward- mechanic brings me diesel for the separator and primes me up and gets me going. I get to a TA and sleep in one of the bays and wait on the head guy to get there and hours later when he does. The separator is looking good and truck cranks beautifully. He still looks at the fuel lines and everything and everything looked good to him. So naturally I'm really skeptical about all this and I'm hoping somebody might make me deal better and bring forth ideas or advice.

One last thing I did speak with the mechanic that showed up at the shipper and his best bet was the seals at the base and the cap of the separator might be bad. That's actually what I pulled into the bay at the TA for but me and the nighttime guy thought we found a leaky hose(the pressure line going from separator to where the bleader screw is)

Thanks so much to anybody who replies. First time poster. You ever hear from somebody till they need help right?