Hi all I have had my Subaru now for about eight weeks having a Focus ST with blufin stage 1 remap. My subaru is a 2008 registerd wrx GB 270. It has recently developed a judder now and again under aceleration esp noticable when I go up a hill.. I have googled this and I get several pos things like faulty spark plugs etc.. How ever it has suposidly been serviced (non Subaru garage) and on inspecting the air filter it apears to have a big patch of black oil substance.. but on checking the air intake both sides of the filter no oil is present.... Anyone have any ideas please..?? Thanks.