AU Falcon Transmission Leak (Major)

Hi, I'm new to the forum and I have had a quick search for this topic but only found EF issues.

I have an AU 75th Anniversary Futura with only 135,000kms on it. It has started to leak very badly from around the transmission "sump". As it has been parked on grass I have not noticed this until now and it has lost so much fluid that it hesitates to go into gear (takes a few seconds to find a gear, and actually lost drive going around a roundabout)

I jacked it up this morning and tightened all the transmission sump bolts which all seemed too loose (between 1 and 2 turns on each bolt) but this doesn't seem to have fixed it as it is still leaking (I parked it on clean concrete this afternoon and there was a puddle of oil too big to be just excess leaking off the underbody)

Also is there any way I can top-up the transmission without taking it to a mechanic, as it seems to be a "sealed unit" and doesn't have a fill point.