Bad transmission installed in 300D, what recourse do I have?

[Sterling30]

I buy a 75 300d this April knowing I may have to have the transmission replaced which turns out to be the case. I take it to this mechanic 50 miles way who usually does pretty fair work at a fair price. I want the job done right so I ask for a price to rebuild and install the transmission which he quotes $1200 but then sells me on a used transmission guaranteed for $800. (Which he never had, he replaced some seal that he thought was a quick fix and showed me that trans he had replaced with black oil around it, that showed the "'original" trans burned out and the seal would fix the leak, only problem was the fluid was the right color and there was no leak.)

And the test drive after the fist fix was identical to the way it ran when I first brought the car in, he never replaced the transmission, he wanted payment for a complete job he obviously thought there was an easy fix for.

Fast forward 6 weeks later and after 3 more tries the car is supposedly done, the transmission installed now had to have the bottom plate that was removed from another transmission and put on the one currently in my car which is significant to note because the 2nd trans ordered never arrived, it was damaged in shipment and I have reason to believe that's the same one presently in my car.

The bottom line is this. The original estimate went from $800 to $1400, I have 30 day warrentee which the mechanic refuses to honor. The trans leaks fluid and will not shift properly, the cost of a properly rebuilt transmission installed will be $1500 - $1800 which was the original plan in the beginning again.

What rights do I have in this situation? The car will be used commercially come this fall and it can't be used in it's present condition. My credit card co may be able to retrieve the costs once the work is done and I present a new repair bill but that isn't written in stone either.

Any and all suggestion will be appreciated.