Mmmmm 1.9 ina a 87? Still, check the rear oil pressure sender .9 BAR,

http://www.benplace.com/oil_pressure_sender_overview_location.htm
http://www.benplace.com/engine/cleaning_pump.jpg

Not sure if the location is the same on the 1.9 bur i guess that yes, they
have a tendency to leak, badly some time.

Also check the rear crankshaft seal, behind the main pulley
http://www.benplace.com/engine/sender4.jpg
on this picture you see the red circle, this is the rear .9BAR sender, just
right of this circle (a bit higher), it's the crankshaft hole, under this
one is the oil pump, another possible leak.

Another possible leak could be the distributor O-ring
http://www.benplace.com/engine/distributor_screw.jpg
# 2 hole on the picture below
http://www.benplace.com/water_pump.htm
In this picture you can see most possible rear oil leak. Unless you have a
cracked engine core.

If i remember correctly, you don't have a oil cooler so tha big O-ring is
out of the question.

Listen to me carefully, go buy 2 cans of brake cleaner and some degeaser,
clean the engine a much as you can with the degreaser and some rug, use the
brake cleaner spray to dry the remaining oil with some towel paper.

Now start the engine and rev it, check for oil leak, if none, go drive the
van for a few mile at freeway speed and check again.

That is why I keep my engine clean as much as I can.

Good luck
Ben
http://www.benplace.com/