Wüsthof Classic 4110 Serrated Utility Knife, 5 Inch

when cutting i.e.bananas/fruit the steel gets very dark an is hard to clean I thought stainless steel is easy to clean/ any suggestions?

How to sharpen this knife, what are the blade angles?

The blade snapped on my knife. How do I return the broken knife for a new one?

I went to cut a carrot and it cut slanted leftward...what's that all about?