At the risk of asking an unanswerable question: how long should i expect the rubber surrounds to last on the older brown 200 woofers? I'm generally OCD about inspecting these speakers which are now over 25 years old. I did think about rotating the bass drivers 180 degrees a few years ago, but there were no signs then of any surround sagging or tears ..... there still aren't. Any reason to replace the surrounds proactively?