Leeward drift

My Scot drifts to leeward especially in light winds. It does this with the centerboard up or down. The forestay is in balance with the jib halyard. The centerboard gasket is in good shape. The bottom is smooth. The leeward shroud was too loose, so I tighted both sides. The problem MAY have started after I did this. Could the shroud tension cause the problem? What else might I try?

If you are slipping in light wind, maybe the main is sheeted in too tight. Let it out a bit until it luffs, then trim it just to the point where it fills and the sail smoothes out, but no more. Just a thought.