I've had success with stop/leak refrigerant for small leaks. I recharged the A/C system on a 1996 Pontiac Bonneville at least 8 years ago and it's worked well since then.
After a GM dealership had replaced a bad compressor the A/C system leaked out over the following winter. They "fixed it" the following summer and it still leaked some. The following year I got a cheap $20 single gage recharging kit with one can of stop leak and UV dye at an auto parts store, (Interdynamics brand #RGM-2CS). I topped it off with regular refrigerant (R134a?). It's not the "proper" way to do it, but it still works fine and I haven't added any more refrigerant in eight years. I'm happy with that.