3 speed gearbox!

i restored a mark1 driver last year and replaceded the gearbox as the origional gearbox has lost first gear.its still got a smooth action on reverse 2,3 and 4 with not notchyness on neutral.
  are they prone to roll pins dropping out or anything silly?,is loosing first gear common?the box oil was nice and clean with no metal chunks.
  any thoughts would be apprietiated as i may open the box up next weekend and take a look (mainly to avoid christmas shopping!)
  regards ,the poppet

Does it go into first if you operate the mechanism directly at the gearbox end? It might be worn or badly adjusted gear linkage, which means that 1st is out of reach.

i tried that.put some mole grips on the selector shaft but the gateway to 1st just isnt there,its solid.its doesnt even begin to slip into a 1st gear,very strange.even ramming it from 2nd doesnt do anything.when i took the box out i found the clutch plate had disintegrated/heat damaged.think he might have been pulling away in second gear until it went bang!poor old golf.