Edited a couple of times for clarity. this post assumes the car is near to be junked, and the OP is looking at desperate levels of repair.
First attempt, is to add a thickener or seal sweller like Lucas transmission fix. That could limp it along for a respectfully decent time. I’ve used Lucas and gotten good results from it, over several years even.
last resort is a tablespoon of brake fluid. ive not heard of this in a while, but back in the day I was told it would cause the seals to swell. It would work well enough for a few days or weeks, and then hemmorage and die a complete seal death throughout the entire unit.
note: the brake fluid hack WILL likely and ultimately destroy the transmission.