Well my Tranny (904) is now leaking!

So i need to get it to a ramp somewhere to get it checked (and find the cause). The leak is at a rate which somewhat concerns me, and has been dripping since the last time i drove the car (No leak before 2 weeks ago). Checking the level yesterday it is below the dipstick!!

So i'll need to fill it to get to the garage!
I've got the 72 Service manual and it stipulates a DEXRON type auto fluid?
Is there a modern equivalent at halfords i can go down and pick up, and if so what is it (any particular rating/numbers)??
Cheers guys.
