Engine/Transmission (1994 - 1998) Fuel Leak

[Rustymule]

My truck stays outside. Back in December it got down to about Minus 25 for about a week. Eventhought I plug it in every night, at that temp it still starts hard, it might turn over 2-3 times, still considerably less than a Ford on a warm morning. Anyway I let it warm up for a couple of minutes and smelled fuel. I popped the hood and the primer pump was leaking a little fuel. All's been fine until about a week ago, and now its getting hard to start. It has a little seepage around the primer pump and so figure its getting a little air. I hear that is just a "O" ring that needs replacing. Does anybody know what size or industry standard number it is? Would like to buy it in town before I tear it down.