heating and ac guys.......i need help.......

ok....i got a 4 ton heat pump at my house, and its estimated to be around 4 years old or so....we bought the house last october and it was here already. this past summer...had a problem with it, neighbor added freon to it because it was low and it was fine. well...apparently,there is a very small leak somewhere that cant be detected with his wand. last night...had to cut heat off(friggin cold as shit here) so it didnt fubar the compressor. my question is....is there any kind of safe stop leak for a home system that can be added to the freon that actually works? i sure as hell cant afford a new unit, so i gotta get this taken care of soon.

by the way..i am now referring to morris jenkins as jesse james. he robbed ya with a gun...they rob ya with a calculator!!