I've had a Waterman pen for over 15 years now and I've just ordered what will be my third converter. I use the pen every day, so you can work out how long they last. The problem with the two previous ones is that eventually the seal where it pushes into the nib unit splits. When it does ink will leak back into the pen casing, through the screw joint and out all over your hands.
Alas there isn't any other choice, except for using cartridges. I used to find I was forever buying them with my previous pen, so I prefer ink bottles. So, I love my Waterman pen, the quality is excellent and it writes really well. The quality of the converter is great too, - except for the pathetic little plastic seal which will go. So, when you see tell tail little ink droplets on the converter when you fill it, take it out and check the seal carefully. If there's even the hint of a little split stop using it and get a new one.
Otherwise you may end up in an important meeting suddenly looking like you're back in primary school after a handwriting lesson.