I have a 2005 Outback, with 6,500klms, it has had the first service & I run on premium unleaded.
Since the car was a few weeks old (I purchased in the summer, so I had the air con on ), I have noticed a foul sulphur smell esp when the tank is between half & half full, to make matters worse the fumes enter the cabin if the windows are even open a chink, it is worse when the car is accelerating up a hill, but can just happen out of the blue notice that the fumes tend to be more around the front of the car when stationary, it seems to just come up from under the back of the engine into the front doors or windows.
The dealership manager & the head mechanic have both been out for a drive with me , they have admitted smelling the sulphur, but they have been unable to duplicate the smell in the workshop the 4 times I have had them look at it.
They now want to swap the catylitic converter from a demo outback that has 4,000klms on the clock.

My question is : Has anybody out there had who has had a similar
experience, if so what did you do?.

do not replace the convertor,have them replace the air/fuel ratio sensor which is the fault.they should have known about this issue by now.

Yep had that problem twice on my '02 Outback, it was the oxygen sensor both times! You'll notice better fuel economy after that also.