Besides the tumbler, there is a spring-loaded detent ball in the rear that can fail (did in my 1984) and the parts jam the key. Not easy to get at since you must remove the lock stalk and pry off a steel cover at the rear. My key works fine without the detents. A lot of work, but throwing it out there.

If I did it again, I would remove the steering lock shaft. It decreases safety and is one more thing to break. I took thieves about 2 days to figure out how to disable steering locks in U.S. cars, so minimal security value.