FYI: it takes longer than a year to lose a spar to corrosion.
This.
I doubt that Piper, nor the other American GA manufacturer's, intended for their legacy airplanes to still be in operation so many decades later. They were not priced, nor manufactured to last forever. That doesn't mean that they cannot be kept in operation for many decades, if good corrosion prevention is begun before any corrosion takes place. I have been asked to inspect several PA-28 series, for the purpose of approving corrosion repairs. In each case, the corrosion could be located along the wing spars in many places (that you could see, there would have been more unseen). None of the subject planes were worth the cost and effort to repair, knowing that if new spars were available, it would be a completer tear down of both wings. Williams has a great reputation, and their work has value, if the plane does.
As can be seen with some magnificent warbirds, any airplane can be restored and kept corrosion free, but it is not a simple, low cost task. All legacy airplane owners need to consider their airplane as having a finite life, and valuing it accordingly. The money invested at appropriate times along the airplane's life will prolong it, but most owners of GA airplanes I have worked with don't see the value in the plane to invest in major restoration and corrosion prevention programs (where warbird owners are more likely).
A client of mine loved is Cessna 210G. I warned him about spar corrosion. He had the inspection done, and it was a major fail - terrible corrosion. Very poor corrosion resistant design on Cessna's part, back in the day (I note that the P210's are way better in this regard!). But he loved the plane, and had invested a lot in it. The last known used center spar was found after a long search. I inspected it, then we had it NDT'd. It was a worthy part. I had to approve a special repair process for the replacement, as Cessna's process was no longer practical. The cost to install it approached half the value of the plane, and end result was really great, but not low cost! While the plane was apart, a number of other defects were found and repaired, that owner knew the value of "maintenance", and flies the reward of his diligence.