From 1967-1991 (24 years!), there were no 737 crashes related to PCU rudder valves. Therefore, it's impossible for it to happen, correct?

Of course, UA 585 happened in 1991 and US 427 in 1994, and it turns out that there was a latent defect that under certain rare conditions, cause a rudder hardover that would make the aircraft impossible to keep in the air.

So, should it have been fixed, or is that simply too rare a circumstance to do anything about?