no pressure...

[Mccaw64]

Recently acquired a old daisy 840 single pump, it functions fine,but it does not have the pressure it should. I've watched all the you tube videos,and it seems that the o- ring on the plunger is the only thing that seals the pressure chamber, is it time for a new o ring?? It doesn't seem to be that difficult to tear down and replace. Ideas? Opinions?

[Clifford]

Never taken one apart but the likely culprit would be one of the seals. If you take it apart it should become more obvious which one is bad.