Iv’e customized an extruder and just added a ring fan around the hotend but discovered that the extra weight has a tendency to rotate the mount about the y axis. This in turn affects the nominal Z height of the hotend and there is some variability there. The height can vary by about 0.5mm which affects bed adhesion. I added a screw to tighten the mount to the carriage but there is still a fair amount of play. Are you seeing Z height variation when you print?