Also, there is a pressure relief valve on top of the R/D - can you check that valve as well as the sheet metal in that vicinity to see if there is an oily residue? When the pressures get high enough, refrigerant will spew from this check valve and then - guess what? The next time you drive the car the refrigerant is now low.

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280