Thank you very much for your comments. Both have been very useful.
It didn't know that the nib could be disassembled and assembled again. I have found some pictures, and it seems that could be probably easy to do so, but I did not try myself. I have contacted Pelikan. They said that it would take 4-6 weeks...
I am still considering what to do. I bought the pen from Amazon, so I will probably go for an exchange.
There is another circumstance that makes me feel tired with this kind of issues. I have received today a grip section that I bought for a Parker Sonnet that had its gold trim corroded and... yes! a nice pair of mould lines there as well. I am very disappointed, as the original old section has no lines at all. So sad.
I will try to polish this section and, eventually, the whole body of the Sonnet. It really needs it.
Anyway. I will forget about fountain pens for a while... After a few disappointing experiences, my conclusion after all is that this is, at the end, a interesting hobby for people that can spend time and money on it, which is not —unfortunately— my case.