At around the 25 year mark, I started to hear a noise from one of my Von Schweikert VR-4 speakers. It sounded like it was coming from a tweeter. I checked and the original tweeters were no longer available (I later found some NOS tweeters on eBay). I checked with Madisound and selected a pair of ScanSpeak tweeters. Installed them and still had the problem. Turns out it was the midrange driver (go figure). An Audax driver that was still in production. Replaced them and all is good.
I actually prefer the ScanSpeak tweeters, so I left them in. These speakers are sitting under covers waiting for my son to have space.