When 8mm isn't anymore
 

Getting ready to change the VCG on an r53 and found a number of the hold down fasteners have corroded to the point that the 8mm socket is useless.
I'm sure this has been covered somewhere? but any suggestions are always useful. I'm going to "drive" a 6mm on one to see if I can loosen it. What say you?

Why would you drop 2 MM? Why not try a standard one size down?

I'd try a standard size and see if it fits, or maybe look into one of those universal fit/stripped bolt sockets to see if that would get those loose. Worst case scenario is if you can get tool down there to cut the studs/nuts and get the valve cover off, you can clamp some vice grips on the remaining bits and wind them out that way.

If it comes to cutting them off, before you do that, use a cutoff disc on a Dremel, and slot them to accept a flat screwdriver bit to try loosening them that way.