dragging whole form via a panel and middle mouse button

for example I have a panel on form.
and I wantto drag the whole form via middle mouse button (mimics middle
mouse button as pressed form caption )
but have no luck with this codes.

(it only works with left button.
but when I put some additional lines (like if (Button = mbMiddle)  ) to
control wheter middle mouse button pressed or not it does not functioning.


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ReleaseCapture;
//SendMessage(self.Handle,  WM_LBUTTONDOWN, 0, 0);
SendMessage(self.Handle, WM_SYSCOMMAND, 61458, 0);

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any idea ?
thanks