If it shifts good and isn't jumping out of any gears, I'd start by changing the tranny oil.  I'd also use one pint of Lucas to replace one pint of the gear oil.

If you've never changed the transmission oil in an old bug, here's something you need to know:  ALWAYS remove the fill plug before you remove the drain plug.  It's never happened to me, but I've heard of a lot of folks draning the old oil and then finding out they can't get the fill plug to turn.