Bruce Yeager from Willmar Air Service is also well versed in Legecy aircraft corrosion. I think Bruce has seen more aircraft come through his (ex) shop then anyone short of Don Maxell or Tom. Bruce has spoken on many occasions regarding corrosion. I have visited his shop and seen a number of aircraft in diefferent stages of corrosion. Surface stuff can be cleaned up by buffing and treating the metal, deeper corrosion can only be fixed by replacement or in the worst case, the aircraft is condemmed.
How do you spot it? Learn the problem areas. Spar Cap, Wheel Well, Wing Walk, Cabin interior, Tubular structure etc. Have a GREAT prebuy done by a Mooney Service Center and specificlly ask them to look for corrosion. Fresh paint MIGHT = covered corrosion so be carefull.
DON'T FALL IN LOVE WITH A PLANE BECAUSE IT HAS A CHEAP PRICE AND GOOD AVIONICS. Dig deeper and if you like it spend the money on a prebuy. If the owner balks, walk away.
If you have a aircraft, don't let dirt accumulate, clean = corrosion free. Metal is treateable in the early stages but go ahead and let that dirt and water mix and sit, and you have the beginning of the end of your aircraft. You are the owner so keep it clean, don't eat and drink in the cabin. I saw the results of a spilled soda on metal under carpet and left to rot. It's not pretty.
CorrosionX is good stuff for the interior areas of the wing and tail cone. It drips forever but it does keep done the corrossion. BUT if you already had a filthy fuel soaked wing and then shoot corrossionX in there, you have done nothing.
Old paint is also a problem if you let the bare metal start shinning through. Bare metal = start of corrosion. Surface at first, white powdery coating, then on to inner grainular. Don't be cheap, keep it clean, keep it painted, keep it waxed and keep it in a hanger. Wash it once in a while, by hand.