There is a fill plug in the side of the transmission (17 mm hex wrench I
believe) and that is where you fill the transmission. You need a gear oil pump
to fill it and the level is when the fluid is at the hole and it won't take no
more. Instead of using a gear oil pump I have "squirted it in" using the gear
oil bottle with a small hose on the top.  Hope this helps.
Ken Herman
86 Syncro Westy
73 Thing