The oil pressure sender unit is trash. My old one leaked at the top of the unit. I purchased a new sender for too many dollars. After only two years the new sender leaks too. Suggest the owner finds an alternative sender unit, ref pg 41, difficult because the XJ-s sender is calibrated for 0 to 100 psi. Most other vehicles use an 80 psi sender. While the owner is conducting  this job modify your banjo bolt, pg 35, because the oil ways do not line up!

Both of my cars leaked oil here. The owner will have difficulty finding the source of the leak because the seal is hidden behind the crankshaft pulley. If oil covering most of the front of the engine, the front crankshaft oil seal is leaking. This repair is a cheap fix, about $20 for a new seal, but this is also a difficult job. I purchased the improved oil seal applicable to later models.

Oil leaks at the rear crankshaft seal too. This can theoretically be fixed without removing the engine, but I put this job on the too difficult list. If your engine is removed for any type of maintenance this is a must do.

The owner will find this a major source for oil leaks. After owning my cars for several months I could not figure out why so much oil spilled onto the exhausts and floor when parked. Reading kirby's book enlightened me to that cam covers have a half moon seal at the aft end of the covers. This seal shrinks and releases vast amounts of oil, especially if the vehicle is driven fast. The only solution is to remove the inlet manifolds and cam covers. The owner must use lots of silicon sealant around the half moon seal to ensure a good seal after the new half moon seal shrinks! Also take a look at the banjo bolts connecting the oil pipes to the cam housing.

At the front of the engine the timing chain tensioner access holes have a rubber grommet. Replace the rubber grommet if its old / hard or missing. This will prevent the oil leaking and will allow the PCV system work correctly.