[dsraven]

I'm with Lee greens way of thinking, use the outside of the old as a form.
Check online for resin and supplies nest you. There are also some videos and tutorials for building a mould and what to use for release agents so the part will come out after. You gotta be deliberate in how you make the form and shape it so it unbolts as a 2 piece form, or else shape it so it is basically funnel shaped, exaggerated, otherwise you gotta wreck the form to get the part out. The form needs to be super smooth inside as any scratch etc in the form will show up on your piece.