Out under the cap, or at the bottom where the distributor goes into the block? If number two, there is an oil gasket that goes under the lip on the bottom of the distributor to prevent leaks, and may be alleviated if you tighten the dist. retaining clamp bolt. If it's leaking from under the cap?????? I don't know what to tell you.
If there's a will, usually there's a way, but then you get to that bolt that you still can't get to with two extensions, two universal sockets, and a contorsionist midget trying to help you.
1999 XJ Four door, mostly stock for now, but I am in the process of building a custom plate bumper.