Soundlab speakers...how reliable?

Soundlab is the one of the best-sounding, least reliable speakers I've heard.
This was true of the A-1s, anyway. High humidity could cause them to arc, burning holes in the panels. They were J Gordon Holt's reference speaker, though.
If you live somewhat arid, though, I say, go for it. They are a good match for OTL amps like yours. Why? I don't know. The results are good, anyway.

Also, you should visit the SoundLab Owners Group (SLOG) website to read what others have said.

Since the introduction of the 'PX' models about 6 years ago, the reliability issues of the older panels have gone away. The improved rigidity of the cores, stability of the stator wiring, and improved insulation of the stators has almost completely eliminated the failures that used to be common. Very few of the newer panels have had to go back to the factory for 'refurbishment'. Additionally, the latest improvement, the Toroid II transformers have improved performance considerably. If were considering used panels, I would insist on getting the PX generation products, and would upgrade to the Toroid II if they didn't already have it. (Disclosure: I am a SoundLab dealer.)

No issues with new models. They will last many, many years. Even the old ones did. I owned several older sets and loved them.

Soundlabs are the best sounding electrostatic loudspeaker I have heard. Twb2 has discussed the improvements and upgrades that has increased reliability. I prefer the non PX panels and have had no issues. Soundlab increased the thickness of the non PX Mylar which increased their reliability. As stated, the Torrid II has made them more efficient and easier to drive. There are 2 different types of backplates offered as well. I recommend the " hotrod version." I own the A3's.