Odd job frustration

Been meaning to tackle one of the house repair jobs for a little while now, finally got the chance (and inclination) today ...

My loo has a problem with its flusher. It's a siphon type that doesn't siphon at the moment. It's broke. (But not icky because I have a workaround that lets the loo function). So this repair job is going to involve either :

Replacing the loo
Replacing the siphon thingy

I'm hoping I don't have to go as far as replacing the loo as I'd have to get someone in to do that for me. And while it's not spotless, it's not beyond my abilities to get it that way. So I've been looking to replace the broken siphon thingy.

But ... (there's always a but). There's a problem.

2 problems in fact - 2 rusty nuts.

To do the repair, I have to take the cistern off the wall to be able to replace the siphon because the bits to unscrew are hidden between cistern and loo. I can do the prep work :
Identify problem & get bits - had 'em ages and I understand how to fit them.
Empty cistern of water - fine. I have a suction pump thingy.
Keep cistern empty - sorted and I can decouple those pipes too.
Get cistern off loo ?

That last is where the problem comes in, there's 2 wingnuts that are rusted to the bolts. I've had them soaking in WD40 on and off for a while but it begs the question :

Why the hell use corrodable bolts in the most corrosion friendly area of a house ? You've got the water, fresh air plus warmth from when you use the hot water. The only place in a house that's more corrosion friendly is the kitchen. Plastic wingnuts would have been far more sensible.

So - frustration today cos those wingnuts just refused to budge.

I'm hopeful I can get them loose though without having to resort to heat. Using heat almost certainly getting a plumber in to replace the loo as I doubt the porcelain would survive. WD40 is usually the universal answer so I'm trying that + time.

In the meantime it's back to that temporary solution which is one reason I've not offered to share the surround sound + movies with anyone lately ...

PS I also have that scent of liquid rust in my nose that the moment that comes with all that WD40 ... with the window open upstairs to take it away too.