Today I changed the oil in the rear diff on my 97 XK8.... I used the hole in the trunk method (making a hole with a hole saw through the trunk wall) . Just have to make sure your hole is in the right place...Suck out the old oil and fill until oil runs out the plug hole.... then make a nice plate with a rubber gasket behind it and a few screws... it will look like it came that way from the factory. All in all pretty easy. I should not have to worry about that for another 100K miles.
Mike in TN