[zabatron]

The gearbox you have is the Getrag B5A.This gearbox is made in Ganzhou,China(under licence from Getrag/Ford) by Chinese company Jianxim.This is basically a Chinese made IB5 gearbox with some minor differences,and they have cut costs by deleting the fill plug.As stated above,you use the reverse switch hole to fill the gearbox with fluid
.To drain the fluid easily,place gear lever in neutral position,and unscrew and remove the selector interlock,(this is the silver/chrome hex bolt with a raised round bit on top, located directly below where the fill plug would normally be on an IB5 gearbox.Once the fluid has drained out,apply sealer to thread of selector interlock and screw it back in(tightening torque is 25nm).Note:only remove and insert selector interlock with gear lever in NEUTRAL position.
Use reverse switch hole to refill fluid.
As for gearbox fluid,I once owned a Fiesta Xr4 with an IB5 gearbox,and I found Castrol Syntrans 75/85 to be the best gearbox fluid for these gearboxes(much better than Nulon,Penrite and the genuine Ford oil).