Lost Reverse in 904. Please help!

Thanks for the replies everyone. It will be a little while before I can pull the pan since I don't have a shop. I use my buddies shop about 45 miles away. One thing I forgot to mention is that it will not roll backward in reverse or neutral with the engine running. Shut engine off it rolls back just fine.

Just remembered one case I saw where the rear clutch pack was burned up so bad it welded itself together and it caused the same symptoms. Only thing is the fluid was burned real bad so that was a clear indicator that the trans was burned up. How many miles does this trans have on it?