I don’t have anything off hand to send you - it’s usually hit and miss when it occurs. Just when I think I’ve solved the problem with a certain mesh something else crops up.
I’ve used the optimize command to some success and try to import models in at a very large scale so that the numerical precision of C4D has enough digits to bring in everything as accurately as possible.
I’ve sent Maxon a number of models over the years when a bad one would crop up. They were even developing a .fac importer at one time and it worked fairly well in some cases - I guess they abandoned it when the guy doing it left the company? …or some such.
I can usually make it passable when I really need to (but hardly use C4D so not too concerned anymore) but am very spoiled at how well EIM exports into EI. My line up usually is Rhino to accept client models in IGES, join and stitch there and export as ACIS, organize in EIM and export from there. Always trouble-free, perfect results in EI.
Or I’ll mesh in Rhino and use the .3dm importer in Modo for half decent results. Rhino is pretty good at times for meshing but EIM’s mesher is pure gold (for EI anyway).