Something that occurred to me while taking of my Timing cover the other day, is that some of the mating surfaces are thin (narrow) and don't mate evenly, in that they overlap each other.
The main culprit on mine is the joint between the Generator Drive chamber and the Oil Pump, which was only about 5mm wide, and mated for about half of that.
To rectify it I had a bead of weld done on the oil-pump (under)side and dressed it down.
It seems to have done the trick
I expect the Cometic gaskets would be wide enough to cater for this, but something worth keeping in mind and checking your own.