Martin Logan Repair and/or Rejuvenation?

I just sold a pair of Martin Logan Sequel II's to a fellow Audiogoner. One of the ESL panels had slipped down about 1/2 inch a long time ago, but did not affect the sound, (at least I did not notice it). I did put that in the ad, and the buyer knew about it.

I shipped the speakers from California to Texas via truck shipping.

When the new owner hooked them up, he noticed that one of the panels (of course, the one that had slipped) sounded a few db lower than the other panel. He said it was really noticable when the panel was run without the woofer hooked up. (The speakers are bi-wired, so this is easily accomplished, although it was something I never did, as I never really noticed it, and neither did my wife or my audiophile friend.) However, I will not call him a liar, as he seems honest, and it is possible, I suppose. (I am not sure how or when this db drop off happened. It might have happened during shipping (he does not think so though), or it may have been a pre-sale condition (This is his hypothesis, I don't think so). Either way, I am willing to help him resolve the problem, including reimbursement of part of the sales price.

My question is this: Have any of you Martin Logan ESL owners ever had this type of problem with a panel?

If so, is there a quick and easy fix or repair?

Or is replacement of the panel the only viable solution to the problem? (This is his solution). I worry that if we replace one panel, that given the age of the speakers (15 years old) that the other panel will then sound different.

I have read/heard of a couple of ideas which range from reasonable to pretty outrageous:
1. Vacuum the panels. I have done this in the past, although it has been years, as general maintenance. (This was originally suggested by a ML tech.)
2. Detach the panels and put them in the shower with warm water running over them to completely clean them.

I know the first idea is reasonable, but does that second solution sound viable? Any help or suggestions would be greatly appreciately by both me and the buyer!