Trans-X for Fluid Leak Causing Slipping and Grinding

I have a 1989/1990 Volvo 240 DL wagon. A couple of weeks ago I was driving on the freeway and the transmission kept coming out of gear. I had it towed to my office (towing company) and one of the mechanics that works on the diesels checked it and said it had no fluid. I’d just had an oil change not 30 days earlier. They put 4 quarts of fluid in and it drove fine for a week. My car started to slip again and my stepfather checked it and said it was low on fluid again. I hadn’t noticed any leaks or fluid in my parking spot at that time. We put more fluid in and I drove it home and kept it parked for 48 hours.

A giant puddle of fluid seemed to be coming out from under the middle of the car towards where the firewall/windshield area under the car (best way to explain location of leak). One of the drivers checked it and tightened a line but said it was overfilled and that’s why it was leaking. I told him that puddle was pretty large and I’m sure it wasn’t possible that there was any fluid in it.

He swore it was too full and I drove the car home. It did fine almost all the way to my place, driving it at 60 on the freeway. About two miles from my house (11 mi from work) it slipped once, and right before I got home it started to make a grating/grinding noise.

My father told me to put Trans X in it.

I don’t know what to do at this point the car only cost $500 and I’ve kept it maintained for 4 years and had parts replaced as necessary but I can’t afford a new car. I’m a single parent, student, work full time and my son has special needs so our budget is stretched to the max.