My wife and I bought a foreclosure condo for use in the summer and part time rental (long weekends, families of college students visiting Chicago, etc.) as it is literally on the beach of Lake Michigan. We are in the process of rehabbing it from top to bottom. Over the weekend I took the vent covers off the two cold air returns (one bathroom, one kitchen) and this is what i found....

I don"t think these were ever removed since the building was built in 1951. There were SO many layers of paint on them...But it gets even "better"...
The backs look like they have never been cleaned. It looked like a a quilt exploded. GROSS!!!
So I spent quite a few hours cleaning, disassembling, paint stripping (two applications), buffing with a wire wheel, and sealing the metal with a clear coat acrylic...

The back louvers were buffed (to remove the rust), painted with rustoleum and reassembled. THEY ACTUALLY MOVE NOW !

One down...one to go...