I have finally capitulated and thrown the bloody thing in the bin, but it can be reprieved if I'm just being dense. I can see mould growing between the rim and the seal, but just cannot get that inner ring thing out. I've tried bashing it with the rolling pin, grabbing at the tab on the plastic ring thing with pliers, swearing at it, throwing it across the kitchen. Nothing doing. Have now consigned most of to the bin, the cup part (which can't just be used as is as has a thread on it) is staying to be used as plant pot holder (I have trouble just throwing things away).