I can't vouch for all the 400 numbers, but I know a couple of 401 who has worked hard for decades, use and abuse, still runs fine. They have bee taken in for service a few times in their lives, but timing wasn't the problem, it has been more of a general care and tuneup than anything directly wrong. I know of a 319 that was knocked out of timing at one point, but it's the owners favorite machine so it was fixed right a way, was in for service once and it hasn't happened again. It would be interesting to know if other repair guys have done the same observations. I see way too few sewing machines to get more than a very limited case by case observation, but the 401 comes off as a sturdy and dependable model from my point of view.