The A/C in my '89 300CE blow somewhat cool, but I'm pretty sure that it needs to be recharged. What is the best way to get it working well again? Some say that R134A would decrease system performance, but I don't think R12 is available anymore at any cost. How about those R12 system compatible replacements? Do I need to replace any components when upgrading? I suppose it would be worthwhile to check for leaks considering the age of the components. What should an average retrofit to R134A cost?