vbCMS Articles decreasing my Google ranking because of duplicate content!?

I was reading some article about SEO, and it just struck me, am I making a HUGE mistake!?

I do a lot of "Promote to article" threads and posts, where I'm practically copying them in vbCMS and making a duplicate content, right? Unfortunately this is something which I didn't pay attention at in the past, and now it started bothering me a lot especially when when I started reading a lot of discussions about that on the vbulletin.com and here.

I have also noticed that my Google ranking decreased, I was number 2 or 3 (sometimes even number 1) and now I'm number 4 on google.com, and what is even worse I'm number 6 at Google.rs (local Google site). (keyword is "satovi")
Another question is how to have evenly good results accros Google.com and Google.rs?

Please advise what should I do in this case in order to decrease the impact of duplicate content?

vbCMS in a link in mainmenu: Satovi - Svet Satova - Satovi
Forum is also a link in mainmenu: Satovi - Svet Satova

Example of the recent article:
vbCMS: Satovi - Svet Satova - Zenith El Primero Stratos Flyback Striking 10th El Ávila sat

Forum: Zenith El Primero Stratos Flyback Striking 10th El Ávila sat

Thanks in advance!

You need to contact vBulletin and resolve the issue. We are sorry but there is nothing we can do to correct CMS issues

I know that they don't have any solution for this, but I thought you might give me some advice on how to overcome this issue. There was some discussion about that already, but I didn't find any concrete solution which I would really appreciate.

Thanks in advance!

CMS basically should be recoded from scratch , current way has no solution at all.

I understand this, but please tell me in your opinion, can this have some significant impact on Google rating?
I posted my question in this topic: https://www.vbulletin.com/forum/show...licate-Content

But as you can see Zachery answered in that thread that this is not duplicate content, which I'm not sure about. Can I at least get your view on this?
I just need to know the truth, then I can start thinking what to do next.

Thanks!

You can simply disable guests to see the comment section. Other than that there is nothing you can do expect using a third party script like wordpress

Thanks for your response, I will try to do that.
Just please clarify, are we talking here about duplicate content or is it something in between?