There are three keys to operating the Sundstrand:
1) Never, ever, ever, ever use Max Flow.
2) Add oil to it every 25 hours. You can't check the oil, all you can do is add until it overflows.
3) Make sure the airplane has the various service bulletins related to additional cooling of the unit. If it's lasted this long, it almost certainly has them, but never hurts to make sure.
I suspect that staying away from hot, humid environments probably helps too, but that's just a guess. And, there's nothing wrong with going to that sort of place occasionally, I'm talking about being based there.
What's your secret, Don? How do you keep it trouble free? Do you do preventive overhauls/services?