Difficult to get Anode Screw off my Mercury

[OrangeCrush]

Hello,

I want to replace the anode on my 2002 2-cycle 15hp Mercury outboard, but the area where the screw sits in is highly corroded. I was able to chip the old anode away, but the screw will not come out and I am afraid I will strip it. I tried vice grips but I cannot budge it. Even if I got it out, the aluminum threads will no doubt be beyond use. I have a new anode but I do not know how I can attach it with the old screw still in place. Do you think I can attach a new anode to the existing screw somehow so that it still functions? Or should I keep trying to get the old screw out even if it is messy?

Thanks,

Jack