I extruded some graffiti-style type and duplicated the results into rings. The result was non-manifold, but I am having trouble grasping the definition of non-manifold (and struggling to use effectively the non-manifold check in C4d effectively). . It seems like extruded shapes should be manifold. My letters DO overlap one another. If I extruded each letter separately, would that solve the issue? I attached the file, in case a fellow C4D user is willing to take a look.