Mine is missing on my nc23
Which of the following should I do?

1) leave it missing.
2) find a used oem one
3) fit a piece of tube with a bung in
4) fit a piece of tube with the end open?

I can’t post pictures on here but it’s the smaller diameter pipe next to the pipe from the rocker cover I’m talking about.

Mine was missing when I brought it so have only seen what they look like on a pdf.

Thanks

The answer is any of the above, The tube is closed at the bottom end and has to be removed to act as a drain so the best option is option 3.
As its on the intake side of the airbox, leaving it off won't affect the running of the bike and it's very unlikely that you will get any water (but possibly some oil vapour) collecting in the airbox anyway