[C320-list] Rusty Transmission Coupler Perkins M30

[Clay Carter]

The propeller shaft on my 1995 comes up from the stuffing box and attaches to a very rusty transmission coupler.  I've noted on my last use, a rusty chunk of the metal from the coupler has broken off--clearly it needs replacing.  It appears this requires sliding the propeller shaft aft so the old coupler can be removed and new installed.  I imagine the stuffing box could be loosened and the shaft slid but the thought of this makes me nervous.  Can this be done with the boat in the water or must it be hauled out?
Thanks.
Clay CarterWe'll Sea #225Alamitos Bay, CA