Example of a Thermostat that needs to be replaced
 

I had some "weeping" coming out the top of the thermostat on my '03 Discovery 2. Not much, but noticeable. Here's what I found when I took off the upper hose. I replace the thermostat and upper and lower hose assemblies. Plan on changing your oil and filter when you replace the lower hoses. Removing the oil filter takes the hose replacement job from impossible to lightly challenging.

https://cimg9.ibsrv.net/gimg/landrov...f6ce8f4e1b.jpg

'03 Disco 2 with 110k miles. New to me. That crushed rim had the consistency of dry, brittle clay. Fell apart in your hands.

Good thing you found it before it got worse.

Is all that orange color from the Dexcool coolant?

Unknown what caused the discoloration. I've only had it for about 7000 miles. It certainly had deteriorated at a very basic/molecular level.