@sifter, take a look at your crossovers. If there is any indication of compromised electrolytic caps, change them. Also look for any indication of excessive heat. I had some old speakers that needed new ferrofluid, and this caused enough heat that the inductor frame warped. Richard So told me that was a classic sign of bad ferrofluid.
There comes a point with these old classics where you have to rebuild or move on.