Bummer.
Using the “PCL5 Compatible” driver instead of the Gutenprint one didn’t help either, I assume? (sorry for insisting, it isn’t clear to me if you did tried that one already).
If none of the available drivers works, I wouldn’t keep my hopes high, as even on the updated gutenprint drivers (5.3.4) I can’t find any reference to that model (or any other LBP one for that matter).
Maybe some other forum user has some tips/workaround to share, like using IPP to send the print job to a CUPS server on a Linux machine (not ideal, but… better than nothing).