It sounds like your lock wasn't hardened properly. That part of the lock is hardened to eliminate the wear of the metal to metal contact and friction that causes soft metal to wear quickly. Some people do a "lock tune up" and file away the hardened part of the tumbler. If the part is not re hardened, the lock will quickly fail. I strip and clean my locks when the snow flies or when I see that it is badly fouled. Grit is the big enemy of that part of the lock and it is only necessary to keep the lock clean with anything that will cut the oil on the lock, a good forced air blow, and a light re lube. Remember that oil catches grit and grit is the same as a file when forced between two pieces of metal.