Wheel alignmaent
It is possible that the front steering triple clamps are distorted. I have had this exact same symptom on my 850. When riding hands-on you did not notice anything wrong until, out of bravery or madness, you released grip of the handlebars. The bike would consistently veer strongly to the left.
I noticed that with the lower steering stem nut untabbed and loose so that the lower yolk could move on the steering shaft, I seemed to get a preferrence for the forks to sit pointing slightly to the left with bars straight ahead. It was difficult to measure but enough to make me invest in new yolks.
If a bike gets dropped on its right side whilst in motion, the steering stop restricts the lower yolk from turning but the leverage on the handlebars is great enough the force the top yolk to twist relative to the bottom yolk. The net result is that both top and bottom yolks twist slightly, levered by fork stanchions, and then hold the fork legs in a slightly turned attitude. With the yolks removed it is possible, using a flat surface, to confirm that some movement has taken place.
With new yolks in place my forks bolted up and aligned themselves and the bike now steers dead straight with hands off. I opted for standard original Norton steel yolks, although they do need a fair bit of fettling to remove the paint masking bits inside the tapers and stanchion holes.