Problem unsrewing lens assembly

[Cameron Shaw]

Would appreciate advice please, mounted 150mm on a lensboard no problem.
Just purchased a Fujinon SWD f5.6 90mm lens for 6x17 use, can not
unscrew the rear lens assembly from the shutter by turning it counterclockwise!
appears to be stuck/locked what do I do to avoid damage to copal 0 shutter?
Techniques? Tools? have no specialist tools for this, have you had a lens mount thread stuck before? The lens is unmounted at present but screwed togeteher with loose lensboard retaining colar. Rear part of lens stuck fast in shutter. Front part easily unscrews !
Thank you for help.
Cameron

[lenser]

If all you are trying to do is reach the inside of the rear glass group to blow off some dust, jut unscrew the front group and open the shutter on B to gain access. If you've got to remove the rear group in order to mount the lens on a board, I would send it to Carol at Flutotscamerarepair.com for servicing. She is very reasonable on price so you will be able to get a complete CLA for what it might cost to just remove the rear group at some shops.

Good luck.