[dss]

...Greyguy, is to first, trace the plane line with the right arm only, no putter. It may be helpful to hold a laser pen, and guide the light on your base line. I think you are still using your left arm/hand to control the takeaway. Second, after you have mastered a true right forearm takeaway, start making backswings with only your right arm, using your putter. Start making 2 footers using only the right arm. Finally, after at least a few hundred right arm only putts, begin putting with both hands on the club. You will realize how irrelevant your left arm is for your putting stroke. I know this will help...it has worked wonders for me.
PS If you haven't already, purchase the "Alignment Golf" dvd sold on this site...watch the putting dvd over and over. Golden information!!