One thing I recommend doing as preventive measure or even performace enhancer.. is to get a tune.. that should be a priority after maintance work.. check out focus-power or fswerks.. not only will that solve your leaning out issues...but it will enhance the performace aspect of adding the header/exhaust/intake...
2000 Turbo Zx3
2003 Pitch Black SVT
2000 SPI 220k miles all original THE UNICORN
Focus Revolution Club