The OP is saying he keeps the lock out of the elements (more than one response has ignored this). But even so, I agree with the "lube it" camp. My Kryptonite U-lock rides strapped to the rear rack with a bungee - yeah, the cheapo plastic mounting bracket gave way after 90 days - as much as I spent for the lock I would have gladly paid another 5 bucks for sturdier mounting bracket - but I digress. In the Summer in Florida it rains nearly every day on my ride home. The lock is rust colored now but still works great. It started to jam on me, but regular infusions of WD-40 have kept it working just fine.

For the rest of you, if you buy one, throw away the plastic mounting bracket. It is useless. You would think someone would have told the folks at Kryptonite by now...