There does seem to be a connection with William, but maybe not what you would expect. My great, great, great grandfather William was apparently married 3 times. 1st marriage to Elspeth Alexandra around 1785. 2nd to my gt.gt.gt. grandmother, Elizabeth Thompson about 1797 and 3rd to Isabell Burnett, 10th Dec. 1829 in St. Vigeans, Arbroath. My great grandfather was a John Buick. His mother was Agnes Robertson and father James Buick. Haven't found any Janet Robertsons in my lot though. I have most of the dates and places for my family tree from 1765 and hope to find out a lot more courtesy of a computer programme I am getting for Christmas! By the way, Burnett does appear as a second name for another William Buick born 5/10/1859 to Alexander Buick and Joanna Stratton. Alexander was my great grandfather's brother. Their other son was James Robertson Buick, family names being handed down it seems. Can you let me have your email address please, for when and if I do find out anything more.
Happy hunting

Gwenda