I took mine in to the dealer for something else, and they volunteered the info on my 420 code, and replaced everything for free. I was floored by their honesty, and I've given them repeat business. Lamoureux Ford, Brookfield, MA.
Old car: '98 SVT T-Red
K&N air filter; Ford Focus RS shift knob. Off to be auctioned off somewhere.
New car: 2003 Honda Accord DX Sedan, 5-speed.