orings dry out . . . hole in 2nd stage diaphragm, etc.
Greetings, time traveler from the 1970s. Let me be the first to welcome you to the year 2013. Among other advances in diving gear that will no doubt shock and surprise you, please note that orings and 2nd stage diaphragms are not made of natural rubber any more. The former tend to be viton or more advanced formulations of buna-n, while the latter are almost exclusively silicone. These things may frighten and confuse you now, but I'm sure you'll adapt to these modern innovations in no time at all...perhaps even attend law school and begin ending monologues with the phrase "but I do know ONE thing!"
But seriously, "hoses leak"? Well, yeah. It's not exactly something you need a tech to check, however. Pressurize the reg. Does it hiss audibly or emit bubbles from the hose and/or hose connections? If so, your hose is leaking; if not, it isn't. "Schrader valves corrode"? If there's one thing on a reg that's unlikely to fail because it's just too damn simple to break, it's the frigging schrader valve in the LPI hose. And like a leaky hose, if it did happen it would be damn hard to miss.
The gist of your post, that some people think their regs are worth more than they really are, is undeniably true. Right now some mouthbreather on fleabay has a ST1 second stage -- no hose, no swivel, and no 1st stage -- up for $700 and when I asked him where the rest of it was he said that was all he found in the storage unit and that it was a steal for a reg that usually cost more than $900. Somewhere between 40% and 70% of new cost is probably a good range, depending on how desirable the reg is, its condition, and what the buying herd had for breakfast the day you list it. But all this crap about 50% dealer price points, keyman discounts on top of that, and the value of warranties and "free parts" programs is smoke, mirrors, and bull
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Mainly, though, nobody needs to hear from you that they've overpriced their regs -- the market will take care of it.