The last time I calibrated the old, partially clogged nozzle, I measured 30mm, adjusted the calibration to suit, and it printed great. And this time, using the new nozzle, I measured 12mm. So that extra 18mm was getting pushed out the sides of each layer and causing the mouse droppings.
I’ll push out a print using the new setting [M93 E241.15] and let you know how it goes.
[Update] The ‘new’ nozzle was already getting constricted, so yet another new one and the print was fine. I’m going to start exploring lower extruder temps, and see how much lower I can get it.