I just got the haynes service manual for my 75/76 250 sherpa t    
Just reading through and it says there is a Gearbox Oil compartment with the filler in the center of the engine at the top and a Primary Chain case filler at the top on the side casing ..  
goes onto say that you stick 300ml's of SAE 10 in the center gearbox  compartment   and 500 ml's of SAE 90 Gearbox oil in the Primary chain case filler  
first off i didnt realise there were two compartments   ..   
secondly  the drain for the primary chain case I thought was at the bottom of that same side casing with a long bolt washer head bolt , I drained 450ml's of oil out of there when I got it  
then stuck the same but new oil back in it ..  
where is the drain for the gearbox compartment ? ?  
also what Oil should I use ..    for the primary I just stuck  Gear Saver 85  in there  
what should I be using for both ??  
cheers