Avoid using ANY stop leak products, as they will likely clog the orifice tube as well as partially stopping any leaks. If you have dual A/C, you're likely to clog the rear expansion control as well.
The system really needs to be evaluated, but it doesn't have to cost a mint. Read the low- and high-side system pressures with a dual-gauge manifold. If it is only low, charge the system with the correct oil (ISO 100 PAG oil), the correct refrigerant (R-134a), and add some ultraviolet dye to make leak detection easier. If the system is completely empty, try drawing a vacuum on it and see how long it holds.
The Delphi compressors used since 1998 are prone to leakage at the compressor case 'O' ring seals. The only way to repair this is to remove the compressor, remove the clutch, disassemble the compressor, and replace the rings.
Before you balk at the idea of doing it right (with a manifold), check the price of a manifold versus one of the "death kits" sold as DIY items. The single hose "death kits" are about $15 (without any refrigerant) and a basic manifold can be had for $45, and it includes the correct quick-connect fittings and safety valves.
http://www.harborfreight.com/cpi/cta...emnumber=92649
Further, you cannot evacuate a system with one of the DIY "death kits" but can with a real manifold. For the price of 1/6th of what a shop wanted to charge for evaluation, you can own the tool forever.
Once you read system pressures, you can decide the best course of action. Until them, you are only guessing, and may become another statistical user of the DIY "death kits" sold as a "bargain" item.