After removing the original pickguard, I glued the crack and clamped the top to form a level surface. Then I filled the raw wood footprint with lacquer and leveled that flush with the finish. I couldn't use a regular replacement pickguard because 1) the top had subtly changed shape over the years and the outline wouldn't precisely line up with the rosette rings and 2) the outline of the original footprint was darker than the lacquer on either side of it. Even butyl cellusolve wouldn't melt this in to my satisfaction and I didn't wish to disturb the original finish with its nice ambering. So I made a new pickguard to match the curve of the rosette and just cover the outline of the original footprint. The new guard is attached with 3M transfer tape, the same adhesive used on new guitar pickguards. Now the pickguard will not cause any cracks and can be reattached without disturbing the finish or top if ever necessary.