Four years ago my local MB dealer, Keyes Mercedes in Van Nuys, Ca analyzed my 1986 190E 16V non-working A/C and reported that they couldn't fix it because there was a leak in the manifold, which would have to be replaced. Total cost for parts and labor about $1000! The other day I decided to take advantage of a Pep Boys special to check A/C systems for $19.95 so I took the car there and their inspection reported no leaks. So they said the system was repairable and also recommended converting to R134-A. An hour later, my car was ready. The total bill for evacuating the system, changing the components for R134 operation and charging it with refrigerant and oil, was $121.00. The A/C is working again and seems to get just as cold as it did with R12!
To think I trusted the dealer who charged me $77.00 just to tell me that it would cost me another $1K to fix it. As a result, I endured 4 summers without air conditioning! BTW, Pep Boys didn't charge for the $19.95 service.