Land Rover Repair: 03 disco oil leak, head gasket replacement, intake manifold gasket

Question
Nigel,
I recently purchased an '03 discovery II. I love the truck, and it is in excellent condition with low miles (56,000). I am having some trouble tracking down an oil leak. I have been using an independent LR mechanic in my area, and so far he has replaced the valve cover gaskets, intake manifold gasket and head gaskets. After all of this I still have a significant oil leak coming down the passenger side of the bell housing. There is no leak if the vehicle stays parked. It is only after driving that the leak kicks in. This makes me wonder if the head gasket replacement was done properly because wouldn't it leak under pressure? Do you have any ideas or suggestions on where to go from here. Thanks.

Answer
I would clean off the residue from the leak and add a tracer dye to the oil so the shop can shine an ultraviolet leak and see from where the leak is coming.  Also, check and make sure the breathers on the valve covers are clear.  if they are blocked, it would cause the inlet manifold gasket to leak continuously.