Dan,
what it boils down to is that you have supplied just a single picture and based on that, I have thrown a couple of suggestions your way.
Again, I will reiterate:
Either way buddy, there are too many scenarios as to how such a thing might happen and they ALL would warrant further investigation!
I can not advise you that the car is worth buying without seeing it myself, hence the advice to leave it alone.
I suggested that you look elsewhere too as I am positive that you will find a clean V very easily. They are not in short supply at the moment.
I will also point out that I am not saying that this one is a shed or is going to give you trouble for that matter.
All I am trying to say is that you have a very limited knowledge on the Evo's so unless you have a professional with you or an enthusiast/owner/trader with knowledge of what to look for as well as some knowledge on what caused this leak to occur, you are better off not going for it.
The other components that could be attributed to having a part to play in this leak include:
Sump Gasket
Air Conditioning Pump
Air Conditioning Hoses
Power Steering Pump
Power Steering Reservoir
Power Steering Hoses
Washer Fluid Bottle
Washer Fluid Hoses
Do you see what I am getting at buddy?
El