>>>*If the tensioner hung up enough to allow the chain to cut the cover it would be warning you with the classic rattling noise.

It is possible the gasket itself breached for some reason, there is a pressurized oil galley that runs pretty close and can leak oil into the coolant.

Typically that would be a chocolate milk color, though, not black. I would dump the coolant recovery bottle and wait, because if you have that much oil in there it should show in the crankcase on on the filler cap for sure.

Run her for awhile that way and see if it keeps coming, watch the oil level, too. Holler if you think you need a cover, 3 year warrenty on those....*EB