Tbh as long as it screws up don't worry to much.... The S1 RST uses the same filter as the 4wd Cossie out of the factory but most people fit the S2 filter (PH2964) you also see alot of S1/2's running Zetec filters (PH5803) as they are larger. I've seen 4wd Cossies also running zetec filters when they have aftermarket oil pressure gusges fitted as they give more clearance as the std filter will no longer fit.