[publius]

I suppose you could use a verey thin piece of plastic sheet, cut to size. Since replacing the entire sight base on something like a MKII is really a semi-permanent thing I wouldn't worry about it. It is something that will never be seen and the factory doesn't do it so I wouldn't. The only thing I would address replacing the sight would be rust. I would put a good coat of grease where the sight contacts the barrel.