Randomly rubbing brakes

I apologize for the lengthy question, but it is complicated. The guys at the Dealership are even out of ideas. So please bare with me.

I recently got a 1986 VW Jetta, Turbo Diesel that I got the breaks re-done on a couple months ago. The previous owners did some really stupid things, like putting break parts on from other vehicles that didn’t quite fit! We took it into Sears (knowing that was a bad move) but it was a weekend and we were in a hurry. They replaced practically everything, including the lines, drums, calipers, master cylinder, and a dozen other things. When we picked it up and tried to leave the parking lot, the front breaks were rubbing. Long story short, they tried at least five or six times to fix it, and every time we picked it up it was the same problem. So finally my brother and I loaded it on his car dolly and took it to the VW dealership. They went over the entire break system part by part, replaced a couple things, test drove multiple times, and after three strikes with the dealership it seemed everything was finally working. We left on a road trip, and all was great until we got a hundred miles down the road, and while cruising at 70 on the interstate they started rubbing again, slowing me down to 60 with the petal to the floor. After messing around for a while I found the only way I could get the breaks to release was to pull the vacuum line off of the break booster. With the breaks released, I then put the hose back on and continued down the road. I drove like this for maybe three hundred miles, with it randomly deciding when to rub before I finally pulled the hose off and left it off. It didn’t randomly start rubbing again.

I have another 86 jetta with a break booster that’s about a year old (which i know works) so I swapped the boosters hoping it might change something. it did not.

The VW techs are at a total loss, and I am out of ideas. I have done a bunch of internet research and have found nobody with a similar problem. Please help!