High g on an antique flageolet

Hi Folks, I’m new here, but I’ve been playing Irish music on whistle and flute for a long time now. I have acquired an antique English flageolet in good condition and it sounds sweet in the first octave but it’s very hard to get the second octave, especially the high g. Any advice about what might be causing this?

Those old flageolets can be really finicky. I have one that barely plays at all.

Have you checked the body for cracks? Cracks can affect different notes differently.

And is it a keyed flageolet? If so, have you tried sealing the keyed holes to rule out a leak due to bad seeling?

Thanks for getting back to me. There are no cracks. I haven’t fully sealed the keys because the lower octave plays well, but I’ll try doing that.