Strange slipping issue..

Still having the same issue. I can power brake it and it makes this noise like something is slipping and it makes a metallic noise. I'm going to get my son to look under it and use a camera to record this. I want to see what is going on with the driveshaft. It's coming from the rear for sure. I'm wondering if the PO had someone change the gear oil and they didn't put in the right fluid.

If it ends up being the rear clutches, does anyone know where I can gets parts for it?