Oil leak only when van is running and appears above the starter . Down 3 liters in 1 1/2 days.

One issue you may run into, when you go to pull down the oil pan, you need to remove the starter, there are 3 bolts directly above it. Another is you may need to improvise like I did to replace the oil pump on my 89'. The oil won't come down very easily because of the transmission pan, the a/c compressor, and the frame connecting to the radiator support. So what I did was put you car up on ramps, take down the starter, the plastic flywheel cover, and unbolt the 2 17mm bolts to the radiator support on the passenger side, then gently pry the beam down and the oil pan should be able to be removed easily.

This is amazing! Play CoC? Visit http://clanshelper.com/ - you receive free C-o-C gems instantly! I just tried that with all my clan! (rC58G3iLTp)

Your engine won't run good much longer if you allow the oil level to get so low the pump sucks air on corners. The oil pressure dropping isn't a guide to how often the oil needs a top up. The idea is to top up before the oil pressure falls, probably checking and topping up weekly would be safer, at least until the leak is cured. In the old days only a fool wouldn't check the oil and water daily...

There are two ways to locate an oil leak. The first method is to wash the area around the leak and run the engine and watch using strong light and a mirror if necessary until fresh oil appears.

The second method is the high-tech method where a fluorescent dye is added to the engine oil and again the engine is run while a strong ultraviolet lamp illuminates the area until the dye appears.

If you have oil running down the side of the block (from above the oil pan) check the lower edge of the valve cover. Those gaskets often fail to seal when the fasteners eventually work themselves loose

Check the fasteners that secure the valve cover to the heads. Torque to 3 ft lbs.

If the leak persists... replace the gasket.

if you look on top of the engine in the valley you will probably see one of the Hpop oil lines leaking at the oring common for the 7.3
the oil runs out the back down to the starter

vacuum leak at throttlebody,check dist.cap wires, bad spark plugs also check vacuum hoses

How many miles/km's you drive in those 3 month's ? oil consumption is normal ! Check when you first start the engine in the morning wetter or not you see a puff of blue smoke, if you see smoke , your valve seals are leaking.
1 liter oil each 2000km is normal.

iits prob a valve cover gasket leaking and running down

cam seals ???