I did a relatively complete refresh, including the hoses. (See
http://forums.pelicanparts.com/porsche-911-technical-forum/757322-84-carrera-c-re-work-mild-climate.html ) My car's hoses bled the R12 out in a matter of months, even if I didn't use the A/C at all.
I replaced hoses, and upgraded the evaporator and front condenser. Still looks stock, as the hoses are the only visible part I replaced. Now running R134a, still blows cold after not being used all winter. (Just tested it a couple of days ago.)