[Bauer_Sucht_Sau]

If you haven't yet changed the transmission oil and replaced the filter, I wouldn't do anything else, until this has been done.
You might have to deal with the vehicle staying parked, until you become the replacement filter and gasket. If you have another car available for daily driving, I would remove the filter and bring it to either a Toyota, Subaru or former Daihatsu dealer. This gearbox was likely used by Suzuki, Mitsubishi and Nissan also. Aisan built automatic transmissions for all Japanese manufacturers. There would be no reason for producing a different filter according to automobile brand. This would be unnecessarily expensive for all brands to do. I would try all aforementioned garages, parts stores and dealerships, until you become this item. Here in Germany, some shop clerks will bring a filter from the shelf for comparisson. Others are lazy and will therefore only serve you when you present a vehicle number, despite the filter itself being numbered.
I'm due myself for a filter repülacement. If you remove your filter and oil pan and then fotograph them, I could then compare both with mine. If they match, I can then find you a source for yours.
The torque converter is a rather simple device. It's therefore unlikely that it has suffered damage and more likely that it isn't becoming enough oil, because of a restricted filter