Exposed aluminum?

[bruckner]

While restoring my problematic ALB/ABS module, I noticed that there are areas with paint missing on the inner rail where the unit bolts on to. I figured that the module leaked slightly resulting in brake fluid running down the rail, a few spots of paint are missing. Question is, any harm in leaving bare aluminum, or should I put some touch-up paint?

 

[Old Guy]

Lots of unpainted / uncoated aluminum parts on the car. Bare aluminum forms an oxide coating fairly quickly which protects it. The aluminum surface would probably be fine as long as there is nothing that can trap moisture against the surface - like a crevice formed by a mounting bracket. A steel bracket mounted against bare aluminum with a little added moisture could create a nice corrosion cell which would be bad. I have a later car so I don't know what the early ABS mounting arrangement is like.

I am presuming that the paint has lifted in a specific area and that you still have painted surface around it. The bigger problem may be the exposed 'paint edge' between the damaged and original paint. I had an older Volvo wagon with an aluminum tail gate. It received a small chip down to bare metal along the lower edge of the tailgate which I didn't notice until the paint around the chip started failing after exposure to a winter of driving. The aluminum was just fine, the paint not so much! So, your aluminum may be just fine; but, if the area gets any exposure to moisture the bond between the paint and the aluminum at that surrounding edge may start failing and the size of your paint damage area may increase. It might be prudent to do some repair work to protect that paint edge. Note that paint repair on aluminum is not so straight forward as on a steel car so you may need to do a little research.