Looks like mud dauber wasp nests.
If it were mine I'd disassemble the parts and clean the corrosion with wire wheel and polish it with #000 steel wool. Then apply a coat or two of Miniwax paste wax. The paste wax prevents corrosion. Don't use car wax because it offers no corrosion prevention.

The paste wax is strange stuff. I discovered this a couple decades ago working on antique radios. I'd wire wheel the steel chassis and polish with steel wool then wax. If I waited to apply wax for more than a few hours the steel would begin to rust. Those old chassis treated decades ago are still rust free.

I found it by wire wheeling the protective coating off of a set of nails and trying various products. Car waxes rusted right away.

http://www.amazon.com/Minwax-78500-Regular-Finishing-1-Pound/dp/B000LNOZAW

You can pick a can up at any hardware store.

I used the same process to clean up my mouse-pee corroded Gottlieb Spirit of 76 score reel:

ScoreMotor.JPG