The chances that the leak is at the shaft seal on the compressor is the best
bet. If you dont know the history of the ccmpressor,the bet gets better.Old
compressors are an even better bet. Cant be fixed  under normal
circumstances. New compressor is best. If you can live with the leak , do
so. A can of r-12 /year? New compressors have a shelf life at the compressor
store of 18 months.Then they should get shipped back to the distributor( if
not sold) for a new shaft seal. It shrinks up if not lubricated.This is why
the owners manuel says to use the a/c in winter.

The schrader valve will leak, but the cap will keep it from being a big leak
, most times. Remove the cap and you can hear the pressure hiss out,
breifly.Probably not your problem, but a bicycle tire, schrader valve
tightener will tighten this up,too. I wouldnt touch it.Leave well enough alone!

The hoses are probably ok. If your leak is large, you can use a soap
solution and look for bubbles at the connections.If you find a leak, tighten
it up a TINY BIT with a  wrench,backed up on the other end of the connection
with a second wrench.Cant soap up the shaft seal.

Best to leave things alone, unless you want to do major repairs. Any opening
of the A/C system is major, costing several hundred if you do it yourself. A
thousand or more if somebody else does it . Maybe $1500.New compressor means
new freon( probably) and reciever /dryer, flushing, expansion valve, valve
cores, o-rings, ( new hoses that you wanted?) and more.

If you have 134a, you dont need new hoses, as the old mineral oil from the
r-12 acts as a barrier and prevents the 134a from leaking out.