On 29/08/2020 16:34, newshound wrote:
I think I would immerse it in diesel for a week. Are the grub screws
out? If so, relatively light tapping should then move the rods with much
less force than it would take to break the casting.

The grub screws are out, I have hit it quite hard, I believe the part
has been sitting in a shed for a few years unused.