WG_moots
My A-M mechanic indicated that the thermostat has been slightly re-designed so the seal is bigger and fits over more of the valve, so it is less likely to come off. Did you notice any difference between the one you replaced and the new one?

 

It was hard to compare the seals as my old one almost looked as if it had been through the shredder.

A new thermostat at the AM dealer is right at $110, I bought the Jag one on-line for $54. The local Jag dealership also wanted $110 for it (they are right across the street from each other, 4 miles down the road from my house).

Even if it isn't the most up to date design, it should hold for a few years ... it is also easy to swap out once you have done it.

Haha, I just read my post above ... it says I bought the thermostat at the Jag dealership. Not sure why I wrote that (getting old I guess). I bought it from Autohaus on-line.

If you aren't entirely comfortable with the Jag part, buy the AM part. It's only $50 difference. The real savings are in doing it yourself.