Middle brace is double skinned so just tipped generous quantities of Waxoil in and caught it as it came out and did it again. Oddly satisfied- All might be rotting around it but that brace is going to be mighty in the future 
Not sure it’s much of a brace as one side is secured by slotted screws. The two either side are fixed with no chance of movement so look like proper bracing. Odd.
What model is that? ND?
No, but they are very similar when undressed so all early ND owners expect the worst in 5 years time!!! You have been warned,
I had a 59 plate Mazda 3 as a daily driver. It was an excellent car and never gave me any trouble. Decent quality interior at the time and never went wrong.
Then after 7 years of ownership and about 75k miles it came back from its MOT at the local dealer with advisories for corrosion on both front and rear subframes and various suspension components…
At the time the dealer quoted £3.5k to get it all sorted, car was only worth £2.5k so ended up getting rid…
They did say it was a common issue on the Mazda 3 so it may be a wider issue than just the mx-5.
I also remember having to get 2 alloys on it replaced under warranty as the lacquer kept peeling after they were only 2 years old. Was told it’s because they are not protected to be able to withstand the salt we use on our roads, as they don’t use it in Japan…
No, it’s a Sport Black NC.
The 10AE alloys were notorious for early corrosion. Any polished and lacquered wheels struggle on salted roads.
i used bondaprimer used it my old tr6 in the late 70s and its still holding back the rust since then see the car last year and it still has all the original panels rust free
Rust-Anode zinc paint is pretty good once you’ve cleaned up the area, but not all top coats like it.
Probably not as bad as it looks? This is going to be a heavyweight area to deal with shunts.
Can’t resist a looksee so I’ll add mine this month.
This is a useful video for getting there. https://youtu.be/za041xyuQOc?si=tCIghEZW4dSf0-1p
When I read about all these rust episodes I get really deflated as I then think that no matter what car I upgrade to, potentially a 2016 onwards ND within a few weeks, that it will all eventually end in rust yet again. My own current MX5 from 2006 is as clean a car as I could have hoped for.
Maybe time to go with another manufacturer 
I think you can’t stuff all Mazdas in the same basket. You said yourself your 18yr old car is good.
Mazda have been consistent in ignoring our small market and salty roads, so it’s just down to luck and judgement getting a good’un.
My ‘06 is looking good too so far. Mayhap it’s a vintage year? 
I think if you are aware of the problem areas and keep an eye on them you should be OK 
I live just 50 meters from the sea that in bad storms actually sprays our house. We have been here for 23 years and cars are sans garage. Never had any problems with paintwork despite waxing only twice a year. All the damage is to the underside. Under the car today and despite it having been settled weather for a few days moisture was all around just hanging there. My three cars are 10/16/18 hrs old.
A decent setup to allow you to comfortably work under any part of the car is essential. My Halford essentials trolly jack and stands has not cut the mustard. About £150 minimum would be my budget would be my guess…
The one on the right was £27 for a pair. An extra ten quid well worth spending - much more flexible in use. You need to use both to appreciate the difference, believe me.
I may not have to replace my Jack but it’s very close to running out of height.
What are the long term consequences of leaving the rear crash bar untreated? I realise it will corrode more, but are we talking about potential MOT failures further down the track or major safety issues?
Probably all of those you mention as being problems if left untreated.
BTW the rear crash bar is a pretty hefty piece of metal and formed to take rear impacts of course. It’s not that that needs treating for rust so much it’s the panel it’s bolted to. Those square rusty patches can just turn into holes. I’ve seen a picture of a badly corroded NC’s rear panel where the crash bar fixings had almost parted company with the car.
My car needs checking there too, a job for this year.