trying to replace the drivers side window assembly in my 83 300td w123 but just realized the horizontal rail that the glass sits in and is attached to the assembly with 2 bolts is completly rotted out,anyone have one for sale??also any leads on window and door gaskets?

Go to a bone yard. Bring some pictures or an old part (make sure to tell the yard crew or they may try to charge you for your old part). Windows and trim did change often so you may (I do not have a 123) have a wide range of years to chose from.