check valve is to stop the reversal of flow causing the rotors to free wheel in reverse when the gas re-expands after a compressor shutdown in order to prevent damage from the thrust reversal.
A second but equeally important function of the check valve is to prevent refrigerant condensing and draining into the compressor during an off cycle. Refrigerant will migrate to the coldest area and in the liquid state is influenced by gravity.
In applications like the RTAA where the compressor is below the condenser, if the check valve is not sealing refrigerant could fill the compressor during the off cycle and cause problems ranging from high motor starting current to compressor damage from the hydrostatic forces developed by the screws pumping 100% liquid.
My advice is if the check valve is leaking change it out or you will be asking the customer to pay for a compressor replacement in the immediate future.