it is likely that there is a leak.
Agreed. You can have them add a tracing gas to the circuit, which pretty soon should tell you (=them) where the leak is, by the use of UV light.
I replaced a number of hoses in my J63 aircon, and felt lucky that the condenser (the extra radiator in front of the engine coolant radiator) was in good shape - as they are expensive as spareparts, and expensive to get fitted.
/Lennart