Car: w211 E200 2006 pre facelift. Converted by the previous owner from manual to automatic.
For context: ESP has been unavailable on this car since I bought it because the steering angle sensor is not working. It just says "ESP unavailable" and "Pre safe inpoerative".

So the story starts 2 days ago when I was about to travel to another city and noticed that my AC wasn't working. Pulled it up into the shop and found out that the compressor was shot. Got the compressor replaced and travelled 200 Miles to a different city. When I was about to reach my destination I did a hard pull and the rear tyres started making a noise like the ABS was locking and unlocking on the brakes and the esp lights started flashing and then went off.

After that I tried to accelerate and the RPM would go up but the car wouldn't accelerate, it would try to go up until maybe 20mph. I only ran it like this for around 500 meters maybe (I know, stupid of me), then reached my destination and when I stopped I could smell something burning and there was smoke coming out of my front bonnet. I looked down and there was a pool of red transmission fluid. I parked the car and looked inside and it was deinitiely leaking but I'm not sure where from, there was a proper trickle stream on the underside of the car but I couldn't pinpoint the source. The next day called a mechanic. The mechanic took a look around and to his surprise, the transmission fluid pipe that goes into the radiator wasn't locked and that's where the fluid was leaking from. The guys who fixed the compressor forgot to freaking lock the transmission line going into the front side of the radiator.

I didn't go hard on my car while I was travelling so the theory is that when I did do the pull near my destination that when the transmission line gave way and the fluid started leaking, which is why the car wouldn't then properly accelerate. The mechanic locked the line, filled in 4 Litres (4,2 quarts) of fluid and tested the car out. Since he didn't have the dipstick on him he suggested that I bring the car into the shop the next day so they can check the levels. That day the car sometimes would not accelerate but if I turned it off and then on it would accelerate fine. When I tried to reverse on a slope it just wouldn't go up.

The next day I went to the shop and they checked with a dipstick and filled another 1.5 Litres (~1.5 Quarts) more since it was still low. After that I have not had any issues in acceleration but the car just doesn't powerslide on U turns anymore, the transmission just doesn't feel light and I personally feel like it's at 90% not at a full 100%. Whenever I pull on turns now the back doesn't slide and obv the esp light does not come on.

There were obviously a lot of stupid decisions taken here but I'm wondering if someone can shed some insight on if my transmission is shot? There are no fault codes related to transmission anymore, we already checked. I still have half a quart of ATF left would it make sense to fill that up as well to see if it makes a difference?