Well, instructions or not, if the cap has come loose enough to drip fuel or suck air, then unscrew it from the bottle, pull it apart, wrap the threads with teflon tape and reassemble. Good as new. Do a leak check in a pan of water just like you would any other fuel tank. I've rebuilt over a dozen UAT's and they're not fragile. I've also seen a few leak, both at the fittings and at the cap. Doesn't hurt to occasionally see if the cap can be snugged up.