1st thing is a compression test, to see if the compression on that cylinder is significantly lower on that side; if so, it'll be new ring time. If the compression checks out, then you'll want to check the valves on that cylinder for too much side2side slop; the V11s have a bit of a reputation for Guzzi using some very fine Italian cheese in the making of their valve guides ; a K-line reportedly will set that problem right.
Best o' luck w/ that.
Thanks Skeeve - that sounds like a good starting point. Because of the lack of smoke at speed I was thinking not likely rings, and more likely your suggestion about valve guides. Not familiar with the term K-line - wussat?