Cleaning exhaust headers.

[calamarichris_imp]

Why am I wrong on this:

the pair solenoid valve lets air into the exhaust during only a small part of engine running conditions. Since the engine usually operates without the pair valve open, anything that is going to happen or not happen to the exhaust valves, exhaust pipes, O2 sensor, catalytic converter, or muffler is going to happen anyway. Pair hose plugged or not.

I never said you were wrong. But the intake valves are also only open for "a small part of engine running conditions"--does the brevity of that part make it unimportant? That brief moment of air intake is crucial for combusting(/oxidizing) the unburnt fluorocarbons etc. before it leaves the muffler. If it remains unburnt while it's in there, it will result in carbon build-up. I've seen both air and liquid-cooled engines with carbon build-up on the valves that eventually killed the exhaust valve seals, which then leaked oil into the exhaust.
It's a relief when you find out that it's just the carbon-encrusted valve seal leaking oil (and not your cylinder rings leaking oil into the chamber), but it's still leaking oil.