I found this cylindrical ring right here in my 2004 disco 2. I think it might have fell from something else and was not there the whole time (at least i hope so), since I did not notice it immediately after I took the valve cover off. What is it, and where does it go?

 

That's a spacer from the valve cover gasket. Each gasket has 4 of those.

Rather, new gaskets have 4. Somewhere there is a gasket with only 3.