This would be a useful DIY as there is a good chance this pump will fail for many of us.

I had one fail at 17,000 miles on a SLK32 (same part number I would assume). And I have one on another of my SLK32s (that makes similar noises to the ones rfourt describes) that has me concerned (starting making noise about 15,000 miles ago at 95,000 miles).

For some, this will create an issue when it comes time to smog the car as a failed pump (and/or associated system) will make it impossible to get a "secondary air system readiness monitor" set. Depending on your state and other factors (some states allow you to pass smog with one "un-set" readiness monitor) this may make your car un-smogable.

Tunaglove, if you have any pictures or more details about your repair that you care to share, I would be glad to see that here. Your speculation about the possibility of premature failure of the pump being caused by excessive pump-running /activity (due to faulty drive circuit) makes sense and would suggest that ALL owners should check for this BEFORE their pump wears out. These pumps are expensive ($500 - $700+ IIRC).

When this seemed higher on my list of projects, I briefly looked for some DIY info (my 17,000 mile pump seemed like as good a candidate as any). I don't recall finding much ...

but, I just looked again and found this
*DIY: Cheap (but not easy) Secondary Air Injection Pump Fix* - MBWorld.org Forums
Chris (tuna) is this consistent with your experience relative to this pump rebuild?

I plan on fixing mine to have a spare on the shelf ... so I will be watching this thread.

Cheers,
Chris