I'm writing a historical work about a German philosopher, in which I use some of his unpublished notes.

One quotation contains an almost untranslatable, hardly intelligible expression - it's not essential to the point I'm making with the citation (which is perfectly clear), but by cutting it out using [...] I mangle the quotation even more.

Can I translate it literally (which turns into nonsense) and write [sic] behind it? After all, it's not what was actually written but my translation, so I feel like this isn't really an option. Or should I chose one of the different possible interpretations that make some sense of it, but thereby pushing some particular reading, even though I don't need that to make my point?