When my car went in for a new pcb for the gauges at Williams they sorted my filler cap. A small sanding/filing of the sharp edges to the plastic inner part. Works perfectly now. The clearance makes both removal/refitting so easy.
Apparently the filler is also used on Caterhams.
A bit hit or miss as to whether any individual filler works ok or is a struggle. Maybe the supplier could modify them to prevent this variable.
Insufficient tolerance or variable component dimensions?
