I hunted around and although I couldn't find a diagram, it sounds like it could also be the high pressure sender as well? It doesn't sound like either should be too hard to fix.

This is where it looks like a lot of oil is coming from, although it's in the same vicinity as the oil cooler gasket which from the responses thus far, sounds more likely. 
http://www.benplace.com/oil_pressure_sender_overview_location.htm

Does the oil pressure switch ever tend to leak?

On Jan 25, 2011, at 11:40 AM, <mcneely4@cox.net> wrote:

> Aaron, the oil filter "housing" may be the "oil cooler."  At least the oil filter fits onto the oil cooler.  There is an o-ring at its base, and this does go bad and require replacing.  At least mine did, and I have been told that it is a common failure.  O-rings for the fix are available from the on-line vendors and from some local suppliers.  mcneely
> 
> ---- Aaron <a.robinson.lists@GMAIL.COM> wrote: 
>> I'm trying to ID and oil leak and figure out how hard it would be to fix. This type of thing is something I haven't done much of..Please feel free to refer me to the bentley. I haven't looked yet, but will be tonight and figuring if I want to take this to a pro or if it's something I can tackle in an evening or two.
>> 
>> On my '87 2.1L van, I've been getting a nice 6" round oil spot under the van every time I stop and spots on the back hatch. Last night I pressure washed the oil-caked area on the front/bottom of the engine (back side of the van) and it appears that the leak is coming from an area above the oil filter housing. I can't see where as it's too tight to see around the heat shield. I also looked around the main pulley seal, and I don't see any oil that's apparent there. I do see a ground wire running to the back area there and it appears that there may be some sensor there.  As I said, I haven't looked at the bentley yet and will be when I get home, but I wanted to get a good start. 
>> 
>> Thanks!
>> Aaron
> 
> --
> David McNeely