The panels eventually need to be replaced. I own a used pair of Prodigy speakers that were made in 2000. I finally replaced the panels on them last year. It sounds amazing now. Both of mine were like you describe, but by using Audyssey on my receiver it made them sound good. It basically took most of the bass out of the woofers to balance it out I think. At the time I didnt know that panels aged like that because I was new to ML. I owned them for about 6 years or so like that before I replaced them.
So since you already own them, you need to contact Martin Logan and see what the price is for a new pair of panels. It shouldnt be too bad for those. My Prodigy panels were about $3000, but those are a lot bigger than what you have I think.
There is also a good thread on here about washing the panels. It shows you how to do it. One member just did it and said his panels sound great now. He used simple green on them. Prior to him doing that I had been told thats a bad idea, but it seemed to work for him. Maybe some of the guys that have washed them will come on here and share some info with you.
I did not try washing mine. I just went ahead and bought new ones. Either way, youll have to take the panels off the speaker frames. You can contact ML for the instructions on how to take them off, or maybe someone on here might have that for you. ML is very nice about giving out info. The best way to reach ML now I think is by email. I want to say the guy youll talk with is named Roger, but my memory for names is crap. Hes very good to deal with.