How to detect leaks

I'm looking at a Cavalier C4-96 (I think) can machine from probably the early 70's. The owner says it does not cool but the compressor runs. It doesn't appear to be rusted.

Do you guys ever use one of those automotive "geiger counters" for detecting freon leaks in cars? Snap-on makes the one I've seen used. It beeps faster when you wave the wand near an active leak. The guy says it needs a charge, I've got a 30 lb tank of freon (R-12) which I bought years ago but don't want to waste it charging a system that I suspect has a leak somewhere.

These system don't just "lose" freon do they? It only escapes if there is a leak, True?

I realize this machine is not a stong collector value, just close to home and I like to tinker on things.

I am not sure how you would check for leaks, but I have the Cavalier C6-174G Model which is a little bigger than yours. I have the manual for it, which also has your model in it, that I purchased from VendingmachinesRUs.com. I am in the middle of restoring mine. I wonder if you have a picture of the side view so I could see what the paint scheme looks like? If you do, can you e-mail it to me. tomtsc@bellsouth.net
Thanks

Whoops, this is a Cavalier CC4-132G, serial no. 539245. The cooling system is model CAV-777C and serial no. 102251. I'm attaching a pic of the side anyway.

Does anyone have a cross reference on what Cav models I could get a replacement cooling system (used, cheap)? Otherwise if I don't have a lead I will not be picking it up.

This is an interesting can vendor with the four motors to release the can and the evaporator is up high in the back.