+1Get an EZ out drill bit from Harbour Freight. It digs in & will remove the old bolt. You could always just drill it out & retap it.
I was gonna say the same thing but then 80 guys hop on and tell ya that they are the best thing since sliced bread so why bother. Take notice the grab it ad is all about screws going into wood. Alum and stainless create a bond after awhile...almost like you weld them together. Then when you finallly break them lose it a toss up if the stainless let's any threads behind in the aluminuim.I have a GRABIT, does not work neither does the one from sears. But your welcome to try, maybe you will have better luck, I always just make worse a mess out of the fastener.