I just painted the valve cover and was putting it back on when the hose that goes on the valve cover was pushed back, and cracked the half dome in the second picture. I assume it's rather important that I get a new part, but does anyone know what it's called, and where I can pick one up, or repair this one? It kinda seems like it's made of some sort of rubber.

imgur: the simple image sharer

imgur: the simple image sharer

 

Engine breather NNB2102AA perhaps?

Egr Valve and Pipes-4.0 Litre-Naturally Aspirated - Parts For XJ Series from (V)720125 to (V)812255 (X300) | Jaguar Classic Parts UK

Item #10 in the illustration

Cheers
DD

 

Thanks Doug. Now I just need to find someone to sell it to me and get it on my car ASAP.

 

Yep Doug is right on. It is the oil breather separator. Some folks have said that it is out of production but I just bought one from Terry's Jaguar for about $18