The problem is not only the turn signals sagging, the rubber spacers that hold the signals to the plate holder end up breaking. I already replaced both.
When I replaced the 2nd. rubber spacer a few weeks ago, I installed a piece of transparent "thick" wall hose between the turn signals, firmly inserted in inside of the rubber spacers. You can't see the hose from the outside. The hose limits the amount of vertical movement, somehow coupling the turn signals together.
Sagging is greatly reduced although I am not certain the solution will work long term, I'll find out in 2 months or so.