I'd check the viscous coupling, if the van has been driven hard enough that
the rear wheel bearings and diff lock are broken...

Jack up one front wheel.  Try to turn the wheel.  It should be "difficult" to
turn.  I'm not sure when the viscous coupling goes out if it locks or if it
no longer locks at all.  Any ideas, Syncro owners?  Anyway, the wheel should 
be difficult to turn.

For the rear lock, it may just be that the vacuum hoses are shot somewhere.  
Cheap fix.  

Front wheel bearings are very expensive as well.  Check them.

You might want to bring it to an independent mechanic who is familiar with
syncros and pay him to tell you what needs to be fixed.  Don't buy the "72-
point Buyer's Inspection" or whatever.  I think they just make the new kids
do those.  They're worth less than the paper they're written on IMO.  Basically
have someone look it over like they'll be getting the opportunity to repair
anything that's wrong.  They'll find a lot of things that are wrong, and a 
lot of things that look wrong that they can stiff you for.  At least you'll
have a better idea than what the seller is telling you, which is likely that
_nothing_ (except the already mentioned items) are wrong.

As far as finding first gear, the shift mechanism seems to be pretty sensitive.
If it gets the least bit out of alignment, shifting becomes very difficult.

I would also get a compression check.

-Jim