Well, between all of the members who have posted, we've covered almost everything. Let us know which item it turned out to be.

possible structural problems related to the unibody not being 100% perfect? That could be an issue, esp with the old datsuns.

I had a problem with vibration when I turned. It ended up being bad tierods. Have you jacked up the front end and tried to shake the tire. Grab it from the sides and see if there is any play. It might also be the axle shaft bolt is too loose.

Blown strut? (Don't laugh guys, just throw'in out a bone there)

Vicky