Crosman 2300T c02 leaking from barrel

My 2300T has developed a leak that is coming from out of the barrel both from the muzzle and breech as soon as the powerlet is pierced. The only place I can see where it can can be leaking from is thru the transfer port. I have changed the o-ring but it continues to leak. Do any of you Crosman pistol gurus out their have any ideas what might be the problem here? Any advise would be greatly appreciated.

Thanks