If they only really show when you put quite a bright light up to it, it's going to be fine I'm sure. I think the only thing it could do is lower the contrast in very bright situations. I have a lens with a similar scratch on the rear element but the images I get from it are as good as I would expect from a new lens. Also Malcolm Taylor (an excellent Leica repair man) told me not to worry about it at all. If you think about it, the scratches only take up ~1/10,000 of the surface area of the rear lens!