I still have my original pair of AR3a that I purchased in 1969.  I replaced the mids (with drivers directly from AR) maybe 22-25 years ago when one went bad. The woofers and tweeters are original.  Although both tweeters have decent output I've often wondered if the sound could be improved by replacing these aging tweeters.  HIVI makes a tweeter that a lot of people seem to like as a replacement and I'm tempted to buy a pair to try.  Apparently they need an inductor as well to sound their best.