Well, by way of preface (although I think I mentioned this in an earlier thread), my roommate “tech bud” is back, after we discovered that the fraudulent charges on my cards were in reality due to the illicit activities of his ex g/f. We found this out when her present (now ex, too) b/f came forward to us both with what she had been very cleverly and stealthily doing – sneaking into wallets and photographing both sides of everything inside. In fact, she had ripped her current b/f off for $3K that way. My bud had wondered about some unauthorized charges on his cc a few weeks ago, but we chalked that up to online ID thieves. Now that we see some of the charges are similar, it all makes sense. 
Anyway, just an example of what a substance abuse problem (heroin in this instance) can do and drive a person to do to others. Hopefully she’ll get some help soon, before it’s too late. 
Anyway, back to the topic … As mentioned some time back, one of the air rails was getting almost untouchably hot on Superblack, and based on what everyone said on here it had to be a stuck or bad one-way valve. So, tech bud removed it last night and OMG. The valve itself was totally gone, apparently burnt away. 
He installed the new one (N.O.S.), and, out of an abudance of caution, I told him to go ahead and remove the other one as well. Turns out that valve looks to still be intact (at least), but apparently nonfunctional at this point. Thank God none of the exhaust gases escaped to the outside in there, or we might have had a fire., or at least fried hoses, belts, etc. 
I am in the process of finding a 2nd valve as we speak.
Some things to learn from this one:
1- Be careful when removing the old valves, as the end attached to the straight part of the air rail is make of thin, cheap pot metal. 
(Jaguar!) … Very easy to just twist it away, esp, with a “well-aged valve” like mine were 
.
2- (b/c of #1), be sure you have replacement valves on hand when you remove the old ones, unless you don’t mind your car sitting around until you get one/some.
3- Be sure to also check the small hose segments leading from the two air rails to the crossover pipe. Both of Superblack’s were also cracked, apparently due to the high heat going through them. (I’m in the process of trying to locate replacements for same as well).
4- From time to time, be sure to hand check both air rails after the car is warmed up, to feel for abnormal heat – an early sign (or late) of valve failure.
5- btw, there was a factory “notice” (i.e. warning) card in the box with the N.O.S. valve, that when r/ring the valves the air switch valve should also be checked, as sometimes a bad switching valve is responsible for damaging the one-way valve(s). We’ll check this possibility out on Superblack, as soon as we find out WHAT the “switching” valve is and where it is located!:
I thought it odd that the other rail, despite the valve being inoperative, never got hot, so we assumed that valve must be good. 
I’m thinking that b/c the other valve was completely destroyed (i.e. missing) that the overall air pressure in the system (due to the crossover pipe) diverted more into that rail as a result, so that in effect resulted in relatively little air flow was going through the apparently good rail. That’s why it failed to get hot.
As soon as tech dude gets a new smart phone (yes, while working he knocked his old one off a stool and broke it ) we’ll take pics of both old valves and I’ll post them on here.
Are there even any good used ones to be had? My tech bud thought about wrapping it up with electrical tape, but can that withstand the heat under there? 
I don’t know why they don’t make a brush-on substance kind of like a liquid form of rubber (or polyurethane?) that can be brushed onto the area of a hose containing such cracks. When it hardens, it would be just as flexible as the original hose material and basically “renew” it on the outside. 
In the meantime, I have bought a bottle of spray starter fluid and have advised that he check the whole engine bay area for vacuum leaks with it (while engine is COLD only), inc. that hose.