rim deteriation

Not sure, But i did the same thing. Took it down to my local mechanic/very good friend, He called me back and said come down and look at this. So i went down and the rim apeared to be alright on the outside but when he took the tire off , there was a very bad stress crack in the middle and went to one side. I crapped my pants. There were no dents or stress on the outside. The rim was junk. Thank god i didnt ride it like that. I mearly just bought the bike and cant stand Michelin tires so i was switching to a better tire when this happened. Now i have brand new tires on brand new black excels. I like them much better. painted my hubs black too.

Is the questionable area near the weld seam? Perhaps there was a run of rims with bad welding...?

It is not unusual to have corrosion and other deposits on the inside of the rim. Yes, if there is a crack; you need a new rim.

If it just looks disgusting, you or they should take a wire brush on a drill and clean the surface so that it can be inspected. There is a slim chance that there is some pitting corrosion. If the pits are not more than 15-25% of the total thickness of the rim, it should be OK. For example, if the rim is 0.150" thick in an unpitted area, and in a pitted area it is only 0.120" thick, that means that the pit is 0.030" deep. 0.030" divided by 0.150" equals 0.20 which is the same as 20%, so that should be OK. These measurements are best made with a point micrometer. Many machine shops have them, but I am not sure of your local dealer. There are also depth micrometers that could be used, but be careful of the curvature of the rim. Also if there are a lot of pits in one area, that can be more harmful than a few that are isolated and far apart. I am curious about what you/they find.

For more than you may want to know, aluminum can have exfoliation corrosion. An area may look like fibers or layers are peeling off. Again, the 15 - 25% depth is a good rule of thumb. But you also have to consider the size of the area affected. If there are areas of a couple square inches, it is time for a new rim. But if you simply have a few small isolated spots it should be OK. Then again, if you really want a pair of black rims, this is the perfect excuse for the wife or parents...safety first.