As I'm sure you've heard there is no Porsche 411.  The Porsche 914 and the 
VW 411 had type 4 motors, which would work in a Vanagon. 

If you get the engine #, a bentley manual (as well as others) can tell you 
the year and size of your engine.  If they PO used all the Vanagon tin and 
schroud (alternator has blower for heat) then you can still tell by the oil 
dip stick.  Vanagon pulls out from the back, 914 pulls straight up.  The 
vanagon motor has more torque but comperable HP to the earlier type 4's. I 
wouldn't be too concerned about the value of your vanagon, as a result.  

Re oil leak.  That's as good as they get!! Don't worry about that little oil.

Martin