You will need to fix the compressor seal, then remove the R-134 fittings if possible. Next you will need to flush multiple times in both directions (to ensure complete removal of PAG or ester), dry thoroughly, and put in the correct amount of mineral oil before charging the system. You should replace all o-rings too while you have it apart. The last step before buttoning it up is to replace the receiver/dryer. Converting back to R12 is a big job, but it can be done and will definitely cool much better. I hope to do my converted 380SE sometime this year.

__________________
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