Hello @DarkStar ,
This is a tough one. I’m going to assume that you don’t have viable low poly topology with clean polygroups to edit the topology directly? If you require this kind of control over complicated forms like this you may want to consider working at low poly. It would be a much easier task to do this if you had deliberate topology to edit with ZModeler.
Clip Curve won’t work in this case because the effects of the stroke are aimed inward and will affect geometry on the other side of the model. I doubt you could achieve very clean results doing this in any case.
LIve Boolean would be your safest bet. That will let you draw out cutting meshes and adjust them all simultaneously with radial sym.
As far as a brush based approach there aren’t many freehand approaches that will work here. The contour of the geometry in that location is too complicated and it would be difficult to eliminate that extrusion without destroying the surrounding surface.
However I do have one unorthodox idea. It requires that your mesh be perfectly radial symmetrical and centered, with the pivot at the exact center. However, in theory:
I notice that the negative spaces in between the spokes contain exactly the clean contour you’re after minus that raised section you want to eliminate. You could theoretically duplicate your model as a separate subtool, then rotate the duplicate so that those “clean” sections of the rim are now located underneath the sections of geometry you want to eliminate.
You could then carefully mask all but the area you want to affect on the original subtool so you don’t accidentally affect the “spokes”, then use the ZProject brush over the raised sections. It will pick up the surface from the underlying subtool and flatten that section down to the surface of the duplicate subtool. You could also theoretically use the Project All function in the subtool palette to do the same thing. Protecting areas you don’t want to be affected with masking is crucial though.
Tip: one way to get polygroups with nice clean edges on a high res model with suboptimal topology is to carefully paint a mask on that section, then use the Polygroups> Group Masked with a high smoothing value. It will smooth and tighten the edge of the polygroup to be cleaner than it otherwise would.
Hopefully that gives you some ideas on how to proceed.