Wow they really got you guys by the short and curlies with this AC fear mongering stuff. HC refrigerant can be safely mixed with either R12 or R134 but it's illegal to do so. No AC shop will want to touch it or they will charge you an arm and a leg to have it 'evacuated and safely disposed of'. If the car was converted to R134 by a shop then the rubber hoses had to be changed to barrier type, as required by law. If the hoses look old and crusty with lots of MB PNs all around then chances are your system was never converted. Whatever you do, don't have it converted to R134. Your wallet will hate you and the AC perfomance will be pathetic.