See the problem with the design is the seal usually breaks the thermostat housing. Replacing the seal won't fix it alone; you need a new housing.
My girlfriend's 2000 just blew hers a couple of weeks ago, and the wounds on my hands from fixing it are almost done healing.
2003 Ford Focus ZX3 2.3l N/A = 221 HP, 162 ft-lbs, email@example.comMPH - SOLD
2006 Ford Fusion 2.3l Turbo = 244HP, 247ft-lbs
2014 Ford Fiesta 1.0; Turbo