This just happened to my '07 XK
 

No idea how or when, any idea what the replacement part is called ?

It is the J gate shifter assembly. Good deals can be found on eBay or a new one from a dealer.

Looks alot like a chemical spill of some sort....bummer... the part new is spendy as you have to buy the whole piece as a unit.... ebay might be your best bet.
BOL

BTW: "Transmission Selector lever Assembly" is what the service manual calls it.

I ended up getting this last night...

07 Jaguar XK Shift Assembly 745681 | eBay

Weird thing is I spilled nothing and there is not a speck of the residue to
be found.

Let us know how complicated the installation is. I know these shifter units tend to have the plastic chrome flake off...

^^^^This is my problem. Can just the bezel be popped out and replaced without having to replace the whole unit?

Unfortunately, no, it's all one expensive piece, as I discovered :(

sigh....figures

Problem solved!
 

Finally repaired it with a piece from Sherwood :)

Clever, and not a bad match!