Hi Wills,
I believe, your Portofino 356502 has the IWC caliber 35110, which is based on the Sellita SW300 movement. Earlier, this reference used to come with caliber 30110 which was based on the venerable ETA 2892-2. Both calibers have IWC's magic onto them making them some of the world's most reliable movements. It is possible that the newer movement has a slightly noisier rotor than its predecessors (experts please correct be if I'm wrong on this). If this is natural, I don't think it will effect the timekeeping reliability of the watch in any way. I have a Valjoux 7750 based 79230 powering my grail, the IWC 3799. It does wobble sometimes, but it makes me feel that the watch is alive! The watch is accurate to +1 second a day and I have been wearing it for 3 weeks straight!
About the line running through the middle of the crown, if you can post a picture here it will be easier for us to understand the issue...
Best Regards,
Sumit