Hi Martin,
My Bridgestone took to diving as well – I stripped the front fork and they contain a spring and two polymer bars. There are three spring variants – soft, medium and hard (race)- the springs have a varying coil gap to ensure the dive is controlled so you don’t slam down.
I spoke to Dan at Moulton and he provided me with a Race (Hard) spring and it is so much better ! and just as comfortable – I can actually pedal out of the stable.
I searched polymer suppliers and you could also buy a bar and cut to size and insert if you wanted to firm up more – trial and error i guess, but I didn’t bother when I realized the hard spring worked.
If I remember correctly the spring is the same as other model.
Hope this helps. I have pictures if you need a breakdown of how it all goes together: templetowers@hotmail.com
Just mail me and I fwd them over.
Best , Will