the complete stranger who turned up at his secluded house in England
At the suggestion of men who fought alongside your grandfather.
somehow is now in possession of the item.
Not 'somehow': because your grandfather sold it to him in the presence of your grandmother.
my Grandfather - who was ill and six months away from his death
Lucky that a doctor was with him all the time that he was with Mr Kochan.
My Grandmother was adamant that she pleaded with him not to part with the item and despite this he parted with the Log Book
Forgive me for pointing this out but it was your grandfather's log book: it was his to do with as he wanted. You may disagree with his decision but it was his decision. Respect your grandfather by respecting his wishes. And stop bad mouthing a man who appears to have done infinitely more than you will ever do to ensure that the bravery and sacrifice of brave men is remembered.