AC not holding freon. Could it be the O Rings? on 2001 BMW 325i

My AC quit working. Freon was added but leaked out.

Asked by for the 2001 BMW 325i
Yes, along with any other point in the system that holds refrigerant. It will be cheapest in the long run to have the system tested for leaks. If you charged it with a refrigerant with dye, you may be able to find the leak point with a UV light.