Car in for 48 month service (the big one) today. I have a GGR back box but currently only have a std air filter. I am thinking of fitting a performance filter but according to my dealer the only one which will not affectmy warrenty (1 yr left) is a Ram Air as this is the only Subaru approved one. Should i do this or tell them not to change the filter and buy an ITG or the like. If i buy a non Subaru approved one what are the possible consquences ie. air flow sensor failures and my warrenty.

All advice appreciated.