They say they have a scanner and watched the O2 sensors, just as recommended; but, nothing surfaced.
They didn't do the latest check (watch the O2 sensors in live data & jump the air pump relay & pull vacuum on the diverter valves), but they're convinced that if anything was going to show-up, it would have with tests they ran.
I asked if they thought the dealer might have other tricks to try, but they were pretty skeptical; these guys are pretty seasoned, ex-Mercedes-dealer, mechanics...they're rarely stumped by anything MB or VW.
At this point, we turned-off the CEL and are waiting for something to surface. The car is up for sale, so if we don't identify it beforehand, I'll offer a discount to fix it when it does happen. Don't know what else to do.
