Hi, I have been reading TT since almost 3 years and now decided to post a message myself.I am a German enduro enthusiast (400 EXC 02) presently living and riding in Santiago de Chile. Reliable KTM factory sources informed me that they do not recommend the stainless steel filter because of a better filtration theý clog up much faster than paper filters. KTM builds in 2 paper filters because they do have a different filtration grade(microns)even though they look the same. It is true that some factory riders use steel filters, but as you are well aware, they do not have to think about maintenance because the engines are overhauled after each race anyway. Please forgive my imperfect English!