Well gas mag O-rings

[dazzer106]

Hi just purchased a well mp5k gbb, was going cheap as the mags where leaking, from release valve at top (so I was told). Question is do I have to replace complete valve or just the O-rings. If either does any one know where I can get valves / O-rings from a as I've searched net but came up with nowt
Chears Darren