Any advice on replacing old through-hulls?

[Brioche]

My 40 year old depth finder transducer and knot meter paddlewheel need replacing, and, in anticipation of that, this winter I tried gently to loosen the old bronze through hull fittings, but they did not budge. Since I did not have replacements in hand yet, I did not try harder, but it would be helpful to hear from anyone who has had experience with removing such old fittings. I have no idea how they are bedded, and whether that has become a permanent bond. They are absolutely water tight, so an alternative would be to simply drill new holes and start over. If I put a big wrench on them, probably I could get them off, but fear that doing so might present me with a major patching challenge. Hearing from anyone who has done this before would provide great guidance. Thanks

[sagablu]

If they are old I would not attempt to reuse thru hole fitting, more trouble than it's worth. The easiest way to remove an old through hull Is to remove the seacock or whatever valve is on there. Then from the outside take a soft wooden plug and hammer it in, You don't have to go crazy. Take a fine saw like a miter hand saw and cut the plug flush to the mushroom. Then with a high quality hole saw that is slightly larger than the opening, use the wooden plug to center it and just cut the mushroom off the threaded portion. Then it is an easy proposition to push or pull the threaded shaft out. 5 minutes of work as opposed to pain and suffering by trying to remove the nut. Just my humble opinion