I'm assuming you are talking about the flicker caused by resizing the splitter's parent control - not flicker caused by moving the splitter. The latter can be eliminated with simple double buffering and the other usual techniques (e.g. set FullRepaint=False and ParentBackGround=False).

I've tried many times to find a solution to this problem (I just wasted all of today revisiting the problem) but always unsuccessful.

The flicker isn't of the traditional kind; The flicker I'm seeing with TSplitter is, as far as I have determined, caused by the way the VCL resizes aligned controls. What it should do is to resize and reposition all the controls in one go and then let them repaint. What I'm seeing is that child controls are resized, repositioned and repainted during the process. This causes flicker as some of the controls are moved, resized and repainted multiple times when the size of their parent changes.