Unknown pen: replace nib?

I rediscovered a 20 or something years old pen which has received some hard handling, and could really need a new nib.
The original nib has taken a solid beating, and looks like it's cracked. The cracked "nib part" is not aligned in the same position as the other half, and if i bend it into position, it will bend back out of alignment when used.

The pen is marked "STYB design" and the nib has STYB ingraved, I have not found any other markings. I don't know anything about this pen, as I received it as a small child (which also explains the unfit handling.) It uses standard international cartridges.

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Attachment 52299

Does anyone know if this nib can be replaced? And do you have any tip for a cheap eBay nib replacement to try in the pen? Or even a cheap eBay pen to purchase just to steal the nib from it?

I looks like the nib/feed part is perhaps held in place with the help of a small "dot" on the inside of the yellow plastic grip section. (Sorry for the bad explanation, English is my second language, and I don't know what to call it. Please see attached photo.)

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Do a search for Styb on ebay. I found this one that looks to have a very similar nib

It also looks very much like a Stypen. I had a number of those, but I'm not sure which size nib they use. It would be smaller than a #6.