It appears that a transition was made from MJA numbered parts (much less expensive and widely available as aftermarket) and C2N numbered parts (50 to 100% more expensive and much less easy to source) in 2003. In the case of the oil cooler for my 2005, which was taller (more rows), and therefore more prone to damage through the lower slot, I changed to the shorter and half as expensive MJA part. Recently, I started changing brake hoses, and ran into the same sort of issue. Up to 2003 the indicated p/n is MJA5670BB for all versions of XK8s, "R"s included. During 2003, the p/n for the XKR rear hose is listed, separately, as C2N3108. After 2003, only the C2N part is listed, and replacing a hose using that p/n is greatly more expensive.
This might suggest that the XKR received up-rated hoses - say, SS armored - and that the opportunity was taken by Jag to consolidate parts, as the C2N item can obviously fit the normally aspirated XK8.
The same thing might have happened with the 4.2 engine getting more oil cooler rows in the "R"s. I don't know anything about XKR rear brakes, so perhaps someone can throw some light. Of general interest to me is what led to the C2N part numbers, and did this all begin with the 2003 MY? What is known about interchangeability? In what other areas might similar things have happened?
Meanwhile, I am ordering an el-cheapo MJA.... brake hose to see if it will fit, and to heck with the $60 C2N offerings if it does!
Thanks.