Thanks guys, I'll start with the regulator.

Found this DIY on the Mercedes forums (I believe it's for the SLK320) and it doesn't look too difficult to change:

Voltage Regulator Replacement DIY- Its usually not the alternator - MBWorld.org Forums

And the regulator looks to be about $40 at the dealer...not too bad, I just hope that's it.

I'll report my luck with the regulator swap.

Thanks,
Brian