Take it to a A/C rebuild facility and have the front seal replaced. Make sure you change the receiver-dryer and attached pressure switches. Make sure they pump the system down throughly before adding freon back into the system. Also check the low/high pressure valves where you attach gauges for a leak. I just replaced mine. You can tell if it's leaking when you remove the cap off of the valve. You will hear a hiss and will also see dye.