Looking for 1999 550 Secondary Air Pump

Have you disassembled it yet?

I'll bet the impeller is frozen in place due to plastic dust build up caused by the impeller rubbing the case. A through cleaning and possibly trimming the impeller will add some life time but it's a rare design with the input tube axial to the rotation instead of tangential as most other pumps are. It's also possible to add a small piece of very hard shim stock in the cover to act as a thrust bearing.

As you know it's also used in some Maserati's and the 355 but I couldn't find any other use.

 

Recently I searched Amazon and I saw a few that looked easy to adapt. No direct replacements but until someone decides to make more a little fabrication is in our future. Who knows, maybe we will trip over a quality replacement. More than Ferrari offered us.

 

I spent many hours searching multiple sites looking for a suitable looking pump knowing that a whole new mount would have to be fabricated without success

Whatever pump is chosen a new pump mount and hose routing will be necessary. I believe it's going to require a bit of thinking outside the box, all of these points are anathema to most Ferrari owners.