I was searching for the Baroile chamber... without success... using an old 1:50k OS map (my excuse, anyway) when I stumbled upon this. Since it looks nothing like Greywether's pics I reckon it must (surely?) be the Rhudil cairn.
With regards the apparent doubt as to this being a chambered cairn (and bearing in mind that, although I've seen a few such monuments in my time, I'm clearly no expert) I would have thought the rather obvious - to me, anyway - capstone [see images] set upon a large, linear cairn makes this a pretty good bet for being kosher. Whatever the truth, the vibe here is fabulous, nice n'secluded, tucked away from the honeypot sites of Kilmartin Glen. Worth a visit for that alone. Hey, perhaps you could even locate the Baroile chamber, too? I reckon I could, in retrospect. But then hindsight does simplify matters, does it not?
Heading from Kilmartin pass the Ballymeanoch stones on your right and, just before Dunadd, follow the minor left hand road signposted 'Rhudil Mill Antiques'... or something like that. Carry on past the house to the end of this road and park in a rough clearing currently used to store 'farm stuff'. A local walking his dog asked if I 'was OK' and was quite happy when I replied I was looking for the cairns... anyway, cross the burn by the handy bridge opposite and trend to the right beneath a tree-crowned crag. The Rhudil cairn lies 'round the corner' to the left. I'm assuming the Baroile version is just a little bit further up. Hindsight, eh?