yes alum will "rust" ... Pure alum is almost worthless as a metal too soft .. I am almost sure that trek dosen't use the pure alum but a alloy .. alum mixed with other metal and elements to create stronger alum. simmilar to a/c and thier structures.

here is a linkhere is a link to alum corrosion

because for the most part this is a block of alum and not a sheet of alum as used on aircraft skin.

also try this link of the way the US military catgorizes corrosion link
its a adobe file.

With all of this being said the frame sould be inspected b/c its a carbon fiber if you recall the Generation 1 carbon bikes from trek were subject to corrosion inspections. and many of them were replaced b/c it had worked its way into the tubes. I would also read the warrenty that applies to your area on a possible warrenty transfer to second owner ect.

To be honest all I can see is paint missing and exposed alum doing what exposed alum dose. becoming dull and forming a film of powder.

If I were buying this bike I would have have it inspected by a trek rep or a reputable shop with knowlege of fiber bikes. to get their take on what is going on with it. ... I would also have the bottom bracket pulled and inspected. if every thing is ok.

take some sos pads. green scrubbie things you uses with your dishes. They come in several grits get the lightest and a few other up from that. Go at it slow with the lightest and work your way up then back to the lightest should pollish up ok ...and clean the area and repaint with clear or color and keep the bike clean I feel the lug is messed up due to sweat or salt water getting at it. this is why it needs to be resealed. A good coat of wax could also help you out here also I keep all of my bikes waxed up so much so it slipped out of my hand and dropped it and put a scrach on it (oh well). I spend extra time with the wax in chipped areas and such.

unless its spreading like in the first picture you should have a few years.

all in all have it inspected by a copentent shop who deals with trek. unless he is selling it cheap enuf it dosent matter then ride the crap out of it untill it cracks out.


have fun.
Kelsey

as far as the oxide clear protective coating .. not exactly it a white power coating that slowely eats away at the metal and pits it.