Working with multi-patch meshes

[ShawnTheSheep1861]

I have an STL with multiple 2D patches that build a watertight closed surface.

My goal is to slice the STL at an arbitrary 2D surface (not planar) which is loaded as a second STL, and export the sliced meshes separately. Information about the patches should be conserved during this process.

What I did so far:

1. Import mesh to slice (mesh1)
2. Import cutting surface (mesh2)
3. Solidify mesh2 using blender
4. Trimesh boolean difference operation between mesh1 and mesh2

At this point I get the error that mesh1 is not a volume or not watertight respectively. How can I resolve the issue while keeping the original patches? The cutted surface should be a separate patch if possible.

Right now, GitHub doesn't let me upload images but if it works I will add them to the issue.