I just replaced mine Saturday and I can tell you first hand the quality of these thermostats is top notch. I've never seen one made this well and I would highly recommend replacing with OEM. The "O-Ring" is not really an o-ring. It actually has a slit that fits around the plate of the thermostat so it seals on both sides. Mine looked literally like new after 170K miles. I only replaced it after I saw the temps going up as high as 198 on the scan gage while sitting in traffic (it's summer in Florida!). I got a little paranoid so I thought be better safe than sorry. It was by far the easiest stat I've ever replaced. Remove radiator cap, Drain coolant out of radiator until it stops, remove 3 nuts. That's it. One tip, though... I had to hold the stat in position with a thin blade from the top while I re-positioned the housing or else it would fall out of place.
Cover belts etc. below with aluminum foil to deflect the little bit of coolant that leaks out when you crack it open.
Part numbers are:
Thermostat - 90916-03100
Gasket - 16346-50010
I'd say 1/3 Banana Job at most.