Just an observation, if it is overfilled wouldn't it stop leaking after the trans case is level?

 

I too have an '04 XJ8 - just recently repaired under warranty for a similar issue. It would leak randomly, sometimes somewhat large amounts (maybe up to 1/2 a quart at a time). Other times it would be fine.

The dealer replaced the transmission sleeve and it fixed the issue. Apparently they have had a few of these fail in recent months, especially on 2004 MY.

Sleeve P/N was a C2C39599, if that helps. They also replaced the pan gasket and pan itself for some reason. I don't think that was related.

Just remember - tranny fluid on the XJ8 is horrifically expensive and hard to top off without IDS.

 

The sleeve mentioned in the previous post is the most common leak. The pan would have been replaced because the filter is built into the pan and is not serviced seperately. No sense taking the pan off and not replacing the filter.

 

I have just picked my car up from Jaguar after having the Transmission Oil Cooler pipes replaced after they were found to be leaking. Might be worth looking at those.