Raul,

Just a long distance guess here but I'd bet that the clutch hub for 3rd and
4th
cracked and shifted.  VW had a real problem with these developing stress
fractures with the orginal style hub.  If your trans is an orginal one then it
will
have that orginal crack prone hub.  The factory has come out with a much
better style hub that is highly resistant to this type of cracking but it will
require
the trans to come out (no small task in a Syncro!) so it can be disassembled
and the new parts installed.  While Syncro transaxles are hard to come by the
parts are still readily available at the dealer.  Expect big bucks!  Remember
this
is a 'physic reading' of your trans but since you still have 3rd, and with the
past
history of this hub, I'd strongly suspect an internal problem.  Sorry!