My best guess, I went a lot of years without a logbook, is 15 years and over 1000 dives on a 1980 Sherwood Magnum. It stopped its trail of bubbles, although it still ran perfectly, so I had it rebuilt, since I was told the parts were no longer being made to solve that issue, I used it for a few more years and got a new Sherwood. I put it back in service when I bought a pony bottle.
To be fair, I always did my own work on second stages, so technically the second was cleaned, serviced, and adjusted as I found necessary. But the first ran, and runs now, flawlessly without intervention. Their environmental sealing technique is great.