The "v4" (blue part in the pictures) was already much tighter, than the (black) stock piece. But it was still not tight enough to print flexibles properly.
The "v5" (depicted in copper) should tackle that now.
My specimen was printed with a 0.3mm nozzle and 0.35mm line width.
You'll need a drill bit for post processing.
> 1.8mm, because the drill will elastically widen the plastic while drilling.
And a sharp knife/scalpel of course.
More on the extruder: