I would recommend to go to a MB mechanic who uses a dye to find the leak. This is specially true with a slow leak in the evaporator. The "sniffers" may not catch it. If your evaporator is leaking, the dye will confirm a leak visually. It is normally seen in the transmission tunnel under the car. If it is not your evaporator, you are lucky $$$. BTW, all the A/C hoses can be repaired since only the rubber portion goes bad. DO NOT buy a new A/C hose. After re-reading your post, I may be too late for the hose.
The compressors are also expensive...
Do a search!
Good luck.