Buying Used Martin Logan Speakers, any concerns?

Depends on the age and of course condition. The older panels get tired. ML suggests upgrading to newer panels at 15 years, and IME, replacing 15 year old panels with new panels makes a positive audible and measurable difference. They can develop delamination issues where the panel attaches to the frame. They can also develop panel dead zones. Both issues will require new panels. Replacements panels may seem pricey, e.g., approximately $2K for Quest panels shipped to you. You or someone would need to install the panels in the frame.

Also the crossovers could need work. IME better crossover parts improve the sound of MLs so, if warranted, this is somewhat of a welcome upgrade.

Be careful with shipping options. Many MLs need to be shipped freight. Older speakers rarely have original boxes so proper crating is mandatory.

Since you've had MLs, you are probably aware of amplifier requirements. This has been discussed here as well as other forums. Worth revisiting though.

Dana Brown, ML Service Manager, has been prompt with answer to my questions. When you find a pair, give him the serial #'s and he'll do a history check.

I've owned Aerius i, CLSIIz, ReQuest, Summit. I bought new and used. I also spent considerable time with CLZ, SummitX, and a few new smaller models.

Good luck.

panels go bad at some point and sometimes faster than you can expect.
they will certainly worth more than conventional dynamic driver.

I had a pair for about ten year with no problems at all. My pair did not have the feature which turns off the voltage energizing the panel when it was not in use (I had to manually unplug it for that purpose). The primary reason for that feature is to kill electostatic attraction of smoke and dust particles to the panel. Even with such a feature, smoke, particularly cigarette smoke, is something of a concern. Smoke can cause a sticky, ugly buildup on the panel. I don't know how much of a performance issue this can be, but, I know of a used equipment dealer that insists on removal of coverings on electrostatic speakers for inspection for smoke damage before buying any electostatic speakers (e.g., Acoustats which have cloth enclosures).

Martin Logan speakers are known to have a pretty impervious diaphragm--the speaker does not arc and burn holes in the panel like quads can do. Martin Logan claims that someone (e.g., a child) can actually poke a hundred holes in the diaphragm without appreciably affecting performance. The main damage conern is actually with the two perforated metal panels on the outside (the stators). If the painted on insulation is damaged, that might be a concern, particularly if the insulation is damaged on the inside of the holes (the closer to the panel the more serious the damage).

I know of someone who had a ML speaker fail because he stored it in a garage for a couple of years in the high humidity of the Washington DC area. The wire connecting the energizer to the panel corroded at the juncture with the panel. I have heard that this has been a problem area in some other high humidity places such as Southeast Asia.

But, overall, these are pretty robust speakers.