[bojan]

Leon, this is exactly what I would and will do.
First, I think their assessment is not correct (taking into account the symptoms I described to them), I think it was the application of "rule of thumb" method.
I talked to them earlier today and the person on the other side told me that "they have their ways of determining what was wrong" and insisting it was the shutter, the argument I did not accept, of course... because he could not explain the pattern : 4 shots, 5th one with error.. I told him I just wanted to understand what could go wrong in such a way to produce such symptoms, and he had no answer to that.
So, next week I will speak with their team leader (he will call me) and I will try to clarify the matter.
The problem is, if it is not the shutter, it will happen again and again..
And, if it turns out it was the shutter, I can replace it myself for much lower price :-)... And I can remove IR filter at the same time....