Hi mate
The fact that there is a pre prepared hole in one of the pieces means to me that this part can be prevented from rotating by the insertion of suitable sized steel rod, while some other part is turned. This then loosens any siezed sections. The more you can get it to rotate the better your chances of overcoming any siezing issues.
Just my 2 bobs worth, and you may have tried this already.
Last edited by twostroker; 16/01/22 05:47 AM. Reason: Spelling correction