you could try this link http://www.gtd40club.co.uk/magazines.php?date=2005-04-01
gtd club magazine spring and summer 2005,Genesis Of GTD Part 1 & Part 2
Brian
21 gearbox oil leak
Ian.
the hole is for the speedo senser,which was fitted to the renault 25 box
the 21 has a cable drive and has a much larger hole,best bet is to purchase
a senser to plug the hole
best of luck Brian.
Ian I believe Renault used this as a anti theft devise that locked the gear box in reverse gear,it just needs a metal threeded blanking plug with washer to seal it off