Torque converter and car slipping 2004 CLK320

[clk2015]

Good afternoon, I have decided to join a couple of online forums with the hope that somehow I can find a solution to my problem. About a month and a half ago I started to notice my 2004 CLK320 slipping and making gravel like sounds, with the slipping specially noticeable when going slow at 20 mph and shifting.
I also did some internet research about coolant contamination that mirrored the problem I had. I took it to MB Santa Monica and had the chief mechanic drive it and he also suggested it might be coolant related. Finally I also had a mechanic who used to work at Mercedez for 20 years and specializes in transmissions look at the car and also thought it was coolant related.
It was decided that the radiator should be replaced and the torque converter rebuild, so last week I left the car at the local shop that I have been using since I bought the car two years ago.
This morning I went to pick up my car, they were just getting ready to test drive it, and when they came back I got the bad news that it was still slipping.
I am truly at my wits end, not to try to get any pity, I am really not trying for that, but I bought that car as my bucket list type of thing trying to cheer me up. I am currently undergoing radiation, chemo, and more for which I need the car, and my out of pocket medical expenses are big even with coverage.
Is there anyone here who has experienced this problems with the car and can offer any help or guidance? It would be very much appreciated and I would be so grateful. Thanks.