Chances are the diaphrams on the passenger side are shot. You can get a complete assembly from the PartsShop, simple matter of removing the inner panel and unbolting the unit then bolting in the new one. Or you can obtain just the rubbers from another aftermarket source. I haven't tried the rubbers yet but am thinking about getting some. I have rebuilt diaphram units using the better rubbers from removed units though.
Since you only have two doors, there should only be one diaphram unit and quite a few less connections.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.