A 1974 that blew cold in 2006 lost its coolness over the winter (stored) of 2007. Now blows warm. No repairs attempted to date. Car basically sits. Compressor rotates freely But it seems to have lost the R-12 charge. Not an R-134 set-up. Are there seals in these systems that fail? I just bought this car from the USA to be imported to Canada in several weeks time. Before being hosed by a GM dealer I would appreciate your hints. Do these units need a re-charge on a regular basis? Is it that simple? The C2s and C3s I have owned have never had A/C so I am a neophyte.