I am not an expert, but since you have received no responses I will offer some help.

Your biggest problem is that you have no idea how much oil is in the system. Additionally since the system was converted, was it properly flushed during conversion or just charged with 134?

If the car were mine this is what I would do; I would break all connections and flush thoroughly, thoroughly remove the flushing agent, replace all o-rings with 134 compatible ones, dump as much oil as I could get out of the compressor, put the correct amount of oil in the system by putting a few ounces in the compressor, a few in the condensor and a few in the evaporator as you reconnect everything (you need to research and find how much oil the system holds) replace the r/d last thing so that the time it is exposed to the atmosphere and the open system is minimized, be prepared to evacuate as soon as you finish replacing r/d, evacuate and charge with 85% of the specified R12 amount. There should be a sticker somewhere under the hood that will specify the refrigerant amount.

If you go to: www.aircondition.com and poke around, you can find the oil quantity, or post a question in the forum and get the answer.

I said that if the car were mine this is what I would do. I take that back. If the car were mine I would flush and do everything I said, except I would put in mineral oil and charge it with R12. MB's just don't have the reserve capacity to cool very well with 134 unless you upgrade the condensor and even then there is no guarantee.

One more thing. I assume that you have found and repaired your leak. You will certainly want to do that before going to all this trouble and expense.

Best of luck,