Here is a picture of the problem on my bike:
It has actually become a lot worse since , to the point where I am actually getting worried for it! Here is a pic I took about 10 mins ago:
Here is fatbelly's one as a comparison yesterday , he keeps his bike a lot cleaner than mine and dosen't ride through the winter so much , I rode every day but it got a good clean every month , at least (and I mean scrubbed with sponge and fairy , gunked the chain and rusty bits , S100 on the bare metal and removed the cowling on at the wheel to clean the engine itself , not just a quick hose down)
You can see it is not as bad as mine but it is starting to come on there too.
It does seem to be a road salt thing but I only got the bike in August! I am actually now at the stage of thinking of taking the system apart to get this bit of metal out and just replace it with a painted bit to stop that happening, it just seems like a very bad area and there is a lot of coolant going through those pipes so it really is an accident waiting to happen.