i will admit. i gave up on 3 bolts. each one going to a finishing mower blade. i ended up taking entire deck to a local tractor dealer. had them use there larger "impact wrench" industrial size of course. and then even a larger bigger breaker bar. with cheater bar included of course. and one of the stronger ones there dealt with it. it took about 15 minutes most of it was "getting a bigger / better tool" to try out. i think it ended up being 3/4? or larger breaker bar with cheater that was approx 8 feet long for each of the 3 bolts.
before i gave up. like you used BP blaster, to a torch, to impact wrench, to box end wrenches with cheater bar. to breaker bar/s with cheater bars. and nothing would give. and things were in such a way, that i could not "grind / drill" the stupid bolts out. so i had to unscrew the 3 bolts no matter what.
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i do not remember the formula of DIY penetrating oil... but it eats paint, eats rust, and gives a little oil... i want to say mutric acid was part of the mix of a couple chemicals added together.
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on inline heaters. (small heater plus water pump) that hook into a couple of the coolant lines never found a good spot to mount them, without them possibly snagging on something and getting ripped off. i have seen multi units have longer cords put on them. but the (small heater / small pump combo) unit always seems to set outside some place either under tractor or off on the side. and right were driving over weeds or possibly sinking front end down in mud / water (up to axle or a little higher) and the unit would get damaged.