This is an unusual oil leak.. I have never seen (or even read about) oil on top of the coils.

If the valve cover is warped - how does oil get on top of coils (on a 6 cyl)? - Not sure about that.

I do think a bad oil filler cap gasket could do it, so check/replace it. BUT it also sounds to me like you might have a lot of excess pressure forcing oil out...What is the condition of your CCV? If old or unknown, you should probably replace it.

Please make sure your mechanic used new grommets. You might also check rest of VCG by running your fingers (w/ rubber gloves) along the passenger rear of engine where Valve cover meets head. That's where it leaks most often and drips on exhaust.

E39touring brings up a good point. The smaller, 3-hole gasket for the front 3 cylinders can slide out of place during installation. I wonder if that is a possibility? but that still doesn't explain oil on TOP of coils.