I'll need to replace the o rings and possibly the plug on a snorkel - does anyone have a parts source recommendation?
B

Try tryphon or pendemonium. They carry the O-rings. As for the hard rubber plug, it's best if you can salvage the current one. If not, you'd have to find a junk pen to get it from. It'll be expensive from retailers. If the plug's just loose, use a little shellac to snug up the fit.

For the rings, check also Tryphon, vintagepens.com and martinspens51.com

edit-- don't forget the point-holder gasket, too.