I have a 1973 450 sl with some leaks in the air conditioner hoses. One mechanic has strongly advised to keep the r12 system, and another has strongly advised to convert it to r134. Any thoughts? Also, the estimates I've gotten for changing the hoses and drier are from about $1,000 to $1700. Any thoughts on this; can I get it done cheaper? I know there would be some under dash work, which is time consuming. Thanks