Caliber called and said that the factory no longer does brake caliper rebuilds and they cannot get the part. Bummer.
Wholesale cost for one new caliper: $668. Ouch.
Lesson of the day: change your brake fluid regularly. I think that the PO did not do brake fluid service and now my calipers are rotted from the water in the old fluid.
Am waiting for pads and brake fluid from mercedesshop.com and will have a go at it myself.
I guess that this means that I have to drive the Mercedes for a while. Darn the luck!