1995 Chev 2500 Silverado

I have a chev silverado 3/4 ton
I just finished doing the exhaust manifold gaskets on the driver side, moving on to the passenger and i noticed 1 of the bolts is broken off, it sticked out of the side of the block very little, I was hoping someone on here could give me a idea on how I could remove this?

its a v8 350


On another note, does anyone have a guess how long sillicone will last as a diff cover seal?

Thanks