It looks to me like you have a rounding problem. Only two decimals might not be enough here.
Did you copy the prims from the other parts?
Turn on "Wireframe" and zoom in really close (by changing "View mode") to the corner, and you'll see that the lines don't coincide into a single vertice.
Did you copy the prims from the other parts?
Turn on "Wireframe" and zoom in really close (by changing "View mode") to the corner, and you'll see that the lines don't coincide into a single vertice.