RC,

Here's a picture, but it's the old o-ring. The new one is red, to match my car color I guess. Our sponsor has them for $2.25 with the same part number 999-707-314-40. The micrometer is reading 44mm.

Before installing the t-stat, I coated it with oil and coated the o-ring with silicone grease.

http://forums.pelicanparts.com/uploa...1307651349.jpg

Good luck,

JT

Thanks JT, the one I have is red and I'll double check it to make sure it's the same size. The mating surface of the thermostat to the case isn't flat all the way around so it scares me, but I guess the o-ring does the job...RC

Green o-rings (Viton) are preferred to red.