If my memory is accurate, I have never had one fail over 15+ years of use. All of our family's original thermarests are going strong (used for car camping mostly these days by my parents) and both my wife's and my 3/4 1" LW T-rest pads @ 10-12 years old have never had a leak with rather extensive backcountry use. The only pad that even appeared to have had a slow leak, thus far, was a BA clearview, but it was no problem to throw a couple of puffs in at 4 am. Additionally, I have not had any leaks with the following, but less use:
- BPL/POE Torsolite
- POE ? w/ inflateable center (like Uber lite)
- Exped 3/4 DAM (older style sans built-in pump)
- Bender's DAM (no legit use yet, though, so no count)
- even old pool mats and canvas air pads used back in the day were fine.
I have kept my gear fairly clean and treated it with normal care and it has served me well. Hiking is all of the US, with some in central america, Europe and W. Asia.
I have a T-rest that came into the gear shop where I used to work about 10 years ago that was a warranty return, which they replaced, but it didn't leak, it delaminated. I kept it around just to play around with and let it live outside of my shed. Last I checked, it still held air, covered in mildew and moss (PNW staples).