A vintage Waterman open-nib Crusader has arrived yesterday. Its nib was described as extra-fine and flexible, though I would call it fine.

I've had a look at the nib and noticed that at the tip, one tine is higher than the other. They might even be overlapping, but I cannot be certain until I find a magnifying glass to have a look. When I look under the nib, I can clearly see the tine that is lower than the other one has been bent before, there's a crease. I think this flexible nib has been abused and creased upwards, then someone tried to bend it back down, but made it too low.

It seems to write fine except twice, out of two full A4 pages of writing, the ink flow almost stopped as if there was no more ink in the pen. The writing turned grey (I was using black ink), but it only lasted for two or three letters, then it went back to normal again.

I would like to know if there is anything I could do about it myself, before I can find a repairer to fix it, and whether I could keep writing with it.

Thank you.

My 52V has a similar problem to your Crusader.

I was advised to use "finger nail" pressure, and lift the tine that is lower so that you can almost bend it back into shape. But only use the slightest pressure or you may damage it. It worked a bit with mine, but there's still a lot of toothiness on the upstrokes.

If the pen/nib is valuable to you or you have not been shown how to fix this issue before I would not recommend self help.
Re-alligning a nib is a tricky and potentially disasterous endeavour for the inexperienced. I have the "nib graveyard" box to prove it.