heavy transmission oil loss on 4 gear automatic gtr.

Hello
I bought an Audi V8 built in 89 a few days ago. He's got full equipment and a gas system in it. But it already has 330000km and the transmission is leaking strongly.
When I picked him up and drove only twenty meters to the trailer he had certainly lost almost half a litre of gear oil.
I picked him up the next day and looked under it. The gearbox is totally oiled down and the worst thing is that the oil drips right on the cat.
Then I unscrewed the air filter housing to get to the gearbox from above. And then I saw that it's oiled from above. So right between the converter and the gearbox.
I once asked work colleagues who "know" what might be broken and they had meant that it was just the simmen ring between the converter and the gearbox.
But today I had called in a specialist workshop once and the thought probably the Wanderl is broken and/or the oil pump leaks. All this fun would cost me around 1500 euros, which is far beyond my imagination.
Can someone please help me find the best way to do this? I'm so cynical at the end...
I am grateful for every informative answer.

Mfg Philipp