GU,GX,& 1P motor codes
020 (rodchange)gearbox 2.0 liters.
020 front transfer box 0.5 liter.
1H motorcode (Rallye)
02C cablechange box code up to ASU 28059 1.9 liters.
02C front transfer box Code up to ASU 28059 0.5 liter.
On the later 02C boxes the transfer box has internal oilways that connect with the gearbox oil supply.
02C cablechange box with code ASU 29059 onwards & all other cable change gearboxes 2.4 liters.
PG motorcode (G60 Syncro)
02C (cablechange box with code other than ASU) 2.4 liters
Rear diff (all Golf models) 0.7 liter.
The correct oil to use is a 75W90 gear oil which can be either a normal mineral oil or a synthetic based oil.
Rear diff drain plug centre underneath, fill plug on left hand side front of the casing here 
btw they are both 17mm allen headed plugs, I made a removal tool from a wheel stud with a couple of 17mm nuts threaded on and then welded up.
020 Gearbox & Transfer box oil filler plugs here
The drain plugs are underneath
The later 020 box has a filler/level plug on the left hand end and does not fill through the speedo cable hole,
please note that the 020 box & transfer box have seperate oil and DO NOT have transfer oilways between them.
the golf 2 syncro 90 and 98 hp (66 and 72kw) 020 drive trains
use GL 4 SAE 80, OR G 50 SAE 75 w-90.
for a Golf 2 syncro the figures are as follows
the g/box takes 2 liters
the front diff a.k.a. transfer box or T drive takes .5 liters
the rear diff takes .7 liters
PLEASE NOTE THE GEARBOX OIL CAPACITY ABOVE IS ONLY FOR THE ROD CHANGE 020 BOX
On this g/box with rod change the box and front diff are NOT connected by oilways and as the front diff only holds 1/2 a liter any oil leaks seeming to come from the centre to right hand side behind the engine should be looked at as soon as possible,
for the cost of the oil compared to the cost of a g/box or diff it is not worth topping up, drain and change it, dont undo the drain plugs until after you have removed the differential filler plugs/speedo cable for the g/box, as it is nice to know that you CAN get the new oil in BEFORE you remove the old oil, be careful removing the speedo cable as there is a plastic gear wheel on the end of it which can fall into the g/box, there are pictures of the drain plug positions for the g/box and front diff posted on site here, the later rod change boxes have a filler/level plug on the end of the main casing behind the 5th gear cover casing, it is the same fitment as on the transfer box but is mounted horizontally.
The rear diff filler/level plug is again an big allen headed plug on the lhd side of the diff case toward the nose, to fill the differential with the correct amount of oil the car must be standing on level ground.