Seized replacement bolt taught me the hard way

[New.age21]

So here's one for the I should've known better file, I was replacing the forward lower chainplate bolt on my Catalina 27 and I figured hey why not swap in fresh hardware, while I had the interior opened up for some other TLC, well I did it and the original bolt came out with a little persuasion, no big deal, I cleaned the hole, hit it with some anti seize, and installed the new stainless bolt
Fast forward to two months, I go to check the tension on the rig and notice a slight leak below that same chainplate, went to back out the bolt just to inspect and… nothing, thing is absolutely frozen in place, Tried heat, tried penetrating oil, even gave it a few love taps, no movement still, I'm guessing dissimilar metal corrosion might've kicked in faster than I expected, even with the anti seize
I'm trying to avoid drilling it out if I can, but it's not looking good
Would appreciate any help

 

[winningbigtime]

Have you tried with a heat gun? A torch get's it super hot, but with a heat gun you're getting it hot enouhg and then cool it off with a wet rag. The temp difference will cause it to expand and contract, so it might let go after a few cycles.

 

[l.d.c.moors]

So here's one for the I should've known better file, I was replacing the forward lower chainplate bolt on my Catalina 27 and I figured hey why not swap in fresh hardware, while I had the interior opened up for some other TLC, well I did it and the original bolt came out with a little persuasion, no big deal, I cleaned the hole, hit it with some anti seize, and installed the new stainless bolt
Fast forward to two months, I go to check the tension on the rig and notice a slight leak below that same chainplate, went to back out the bolt just to inspect and… nothing, thing is absolutely frozen in place, Tried heat, tried penetrating oil, even gave it a few love taps, no movement still, I'm guessing dissimilar metal corrosion might've kicked in faster than I expected, even with the anti seize
I'm trying to avoid drilling it out if I can, but it's not looking good
Would appreciate any help

Anti-seize helps but it's not foolproof in a marine environment! Before drilling, try a shock load with a well-fitting wrench. A sudden, sharp turn might help break it free! You could also try tightening the bolt a hair before loosening. This sometimes disrupts the corrosion. An impact driver might also work, providing both rotation and impact. If those fail, a longer soak with a more aggressive penetrating fluid over a few days might be your next best bet! I hope one of those would work!