Before you spend any money mate get it chrono'd this will tell if it is definitely down on power. All gas rams are affected my the cold weather and your rifle could experience a slight power loss if cold for prolonged period. However, if the power is down the most likely cause is that the ram has lost air, you can either get it pumped back up (gunsmith or somebody who owns pump) or get it serviced at theoben (£69), the service will address any potential issues with worn seals etc. Great guns the fenmsn.