You have received some good replies and on the right track. The AC shops can recover the R12 and repair the hose if that is indeed the problem.
One other thing. Some A/C shops, in spite of the fact that it is illegal for them to tell you so, will tell you that it is illegal to top off an R12 system. They will do this in an effort to sell you a conversion job.
In the 609 Certification test they are clear about this. It is NOT illegal to top off an R12 system. That said, diagnose before you act. They can put in UV dye and determine for sure where the leak is located before doing the work. They have other valid means of detecting leaks.