Painting - Restoring or painting anodized window frames

Our window frames are anodized and dark brown in color...they have become tarnished over the years to the point they are ugly....there is no longer a uniform color to them. I am not sure what caused this...probably oxidation....over a 20 year period of time.

I am wondering if I should attempt to treat them with TSP or other chemical in an attempt to remove oxidation or whatever is causing the mottled look...
or should I consider painting them using a auto-quality urethane paint (after priming with an acid-etch primer). Since the windows have a southern exposure and take quite a beating with UV rays, etc....only the most durable paint will suffice and I believe that is the urethanes sold by Sherwin-Williams and PPG Paints.

Any thoughts here ?

I would just sand and clean. Latex paints usually hold up the best in the sun. Use of a good brush and thinning the paint with floetrol should give nice results. Personally I think automotive paint would be over kill although it will give it a finer finish.

do you agree a special etching primer is required for this job ?
The finish must be perfect...that's why I think a urethane sprayed application is the best here....

90% of all alum windows I've painted have been with either latex or oil applied with a brush. The rest where painted with a spray can. I never used a primer - just sanded as needed and cleaned well. I never had a customer [alum windows] that needed a perfect finish but all were satisfied with the results.

For a perfect job you would likely need to sand and clean, spray a primer, sand and then spray finish.

MERRY CHRISTMAS