Smith & Wesson co2 seal

[Ray]

Hi All
My mate has bought one of the above and only gets 25 shots from a Co2 bulb.
There is a slight hissing noise comming from the grip and I think the small orange seal has gone.
I have just picked one up from on here and get 50 shot from a bulb no problem.
He did say that he screwed the bulb in as tight as it would go and it still leaks.
I said it should not be that tight and he has probably damaged said seal.
Can anybody let me know the right seal to get and where to get them.
Thanks in advance Ray