A Plus 2nd gears are marked with a single identification groove.If you are about to undertake a gearbox strip down and you are using an old Haynes manual beware. When locking the gearbox into 2 gears to undo the large mainshaft and 1st motion nuts, lock your gears into 1st and 4th. NOT 2nd and 3rd as stated in Haynes manual as you could very easily strip your laygear or 2nd /3rd gear.