Offsetsrf failure on complex polysurface

Oke guys, I need help concerning offsetSrf. I designed a device curved to follow the shoulders. For prototyping I am going to cast a silicone cover with a thickness of 1 mm. So what I need to do is model a mold, and for that I need to offset the entire device uniformly with 1 mm. (and also a version with 5 mm)
Offsets that I tried get holes or messed up surfaces and therefore are hollow (I know, the model I made is quite messy…) It needs to be a solid as I need to booleandifference it inside a cube to get a mold.
Scaling does not work as I do not get a uniform layer of 1 mm. Neither does Shell or offsetmesh and other things that I tried.
As the device is already 3D printed, I cannot make a lot of changes to the base model.

Is there any way to clean up the polysurface and/or make the offset work?

Lia for mold.3dm (10.0 MB)

You would save the day of a young product designer!

I’m not particularly knowledgeable with 3d printing, and that file sure is big ! Have you tried individually offsetting the 3 different parts, it worked on my machine, the end end sections took a minute or 2 to offset, the junctions where the ends meet the central section looked like they may need cleaning up though

Yeah I know it is big, it needed to be bent over the 3D file of a torso to fit.
And yes I also tried that. Even dividing the end section in parts. Actually that junction area that you mentioned where the device narrows down is indeed where the issues are. There are 4 missing surfaces in the resulting offset. I do want to clean up the model there but as far as I know I cannot create edit points on a polysurface… Is this possible?

personally I’d rebuild it, it looks ever so messy