I seem to have a leak or two each time I mount up a set (although I got lucky the last time). I put soapy water, actually I just spray on whatever I have close in a spray bottle, all the way around the bead to make sure there are no leaks. Mostly it's getting everything clean, any debri will cause a problem. I've only had one stubborn one, and I got it to seal by putting some tire patch glue around the bead.
18 lbs sounds like a lot, is that the torque that you're instructed to use on those wheels? I would NOT over torque them. The bolts can break later on, one by one, and cause you a problem, possibly a serious one. There is a lot more torque applied to those bolts if some start to break, they can only handle the force on the lock ring with all of the bolts sharing the load.
BTW, I recommend always using new bolts when you take one apart. I learned this lesson the hard way. The bolts can get over stressed when taking the ring off since we're not as careful with removing them as we are installing them, and then break as they are re-installed. I've had to easy out a bunch of broken bolts, which isn't always easy with grade 8 bolts.