Hello John
May be daft reply but do you know the grip is actually 2 parts it sounds to me like the 3 dowels are a bit tight
On yours. Tried to take a picture but it's too big.

Mine came with a tube type spanner that has got 2 tongue prongs that fit on the end of the filling nozzle. If you take
The dust cover off you can see 2 slots in the black tube that is the nut holding the grip on