BigToe - Good point and I agree. I don't think I'd want to chance Nylocks anywhere near the exhaust. There was a study that was completed years ago that found the optimum holding torque value was just below the yield point of the threads. This makes the fasteners a one-time use, similar to head bolts.
One of our biggest challenges for space applications is outgassing. Polymers, nylons, etc. all tend to outgas quite a bit of volatiles and for a long period of time. This can create problems for our optics and other sensors. Otherwise, we'd probably use Nylocks (but not near the exhaust of the thrusters... :)
Phil