I have a number of fountain pens, but my favourite is a Sheafer PFM (Pens For Men) Snorkel that I bought new in New Zealand in about 1972. It's fitted with a broad 18 carat gold nib, the body is burgandy and the cap is brushed stainless steel. I think that this combination was only available in Australasia. It's usually filled with brown ink , my current favourite being 'Lie de Thé' by Herbin.
Anyway my question is, how long will the ink sac last before it needs to be replaced, and how do you replace it on a snorkel?