Peter
Just spent 2hrs on this pen and non the wiser. If you remove the blue rubber complete with the brass holder you can store your spare leads and that it.
On turning the lead out there is still about 1/2" of lead still in the nib when fully pushed to the end of the mechanism. The only way I can find to put a new lead in is to take the pen apart . The PENKIT Uk Sierra Pencil Assembly Insructions doesn't work eg it mentions push the button on the the Finial end until the lead is exposed, what button thought it was a twist pencil.
I have emailed Tony at Penhits uk but he is away till the end of the month
Glen