Disco 1 Auto box problems.....

Hi folks, as the title says I have a few issues with my 300tdi auto box.
I used the old girl to pull a trailer and a series 1 back to mine a couple of months ago, journey of about 50 miles.
On the way to the pick up it started searching between 2nd / 3rd. Anyway managed to get the series loaded on to the trailer after a bit of messing around. Tried to pull the trailer out of the field, to wet and muddy, had the old girl in dif lock, lots of spinning etc etc. Ended up being helped out with a tractor.
Got back on the road, about ten miles in it really started slipping between gears pretty bad. Then. Lost all drive and it dumped all its fluid on to the road. Looks like it came from the bell housing area.
Got towed home. I refilled the box to drive it in to my barn, and off it went. I took it up the lane to see what it would do, all fine until I'm guessing it started running low on oil again. Then lost all drive. Refilled again and drove it in to the barn!

So what to do?.
Would it be as simple as a gasket between the bell housing and the block?.
I have removed the cross member and most of the bolts from the housing but am wondering if I need to remove the box completely or is there something else I could try first???

is it an oil cooler pipe on top of bell housing or actually out of bell housing, if it is out of bell housing its most likely the seal ,depends on what caused the seal to fail ie t/c or excess pressure,worth a look ,theres a brass bush supports t/c behind the seal also

Thanks James, as usual!.
It is coming out of the bell housing, so I'm looking at the seal failing!.
Think I may have mentioned before but when I replaced the head gasket I found the breather, right hand side, didn't know what it was, put a bolt in the end to seal it off!.
I'm guessing this could be a reason for pressuring the box enough to blow the seal???

could be if breathers blocked