I noticed some (very little) oil dripping from the differential of my
'90GL, so I thought I'd check the gear oil level.  I looked up the
relelvant info in Bentley and Haynes, grabbed my socket set, and rolled
under the van, ready for action.

Well, I was ready for action except for the fact that I don't know what
kind of tool I need to remove the plug.  It certainly isn't in my socket
set.  Is that a hex nut?  Anybody know what size?

thanks!
--sharks