.<snip>  Is there a bolt that just needs tightening or is this more
serious? <snip>

Pop the little cap off at the base of the wiper arm.  Undo the 10mm nut
and lift the arm off (the inside of the arm base is soft metal and the
grooves get cut into it when the arm is tightened on to the wiper motor
shaft).  Properly position the arm and push it back on the shaft.
Reinstall the 10mm nut and tighten.  That "Should" cut new grooves and
allow the wiper to function correctly.

Some have reported using a bit of steel wool when there was no longer
sufficient soft metal to work with.  I have not tried this but it sounds
like it might work.

Hope this helps.

Mike
'84 GL 7pass auto
'85 GL Westy manual