Mine is the newer painted chassis 4/4 and so far I’ve managed to keep corrosion at bay. I did paint some of those bare steel parts fairly soon after purchase and that’s really helped, some of the more intricate parts i’ve periodically sprayed with aerosol waxoyl, also proven to be a good move.
I’ve not needed it on the Morgan but I’ve been using hammerite krust on our forty year old lotus, it’s a great product, lightly wire brush any loose rust hen lash this stuff on and the remaining film of rust turn black and forms a hard protective surface. Used it on my Caterham too and it’s been perfect since.

Some OE brake disc manufacturers coat them with a sort of hi temp zinc spray, it gives a nice satin grey finish that lasts quite well

https://www.ate-brakes.com/products/disc-brakes/original-ate-brake-discs/coated-brake-discs/

Hi Jon, on the Plus Six the brake disc itself does have that grey finish and it seems to have lasted quite well and protected the non braking areas.. The disk is secured to a disc carrier by a ring of nuts and bolts. The disc carrier is well finished and seems paint protected and has no sign of any corrosion. The carrier is then held to the front hub mainly by the wheel studs that pass through it and one small countersunk hex fastener which looks to be a locator. Its just the hub that is not corrosion protected. I have now done the same as you and neutralized the rust on the hubs and covered the hubs with a coat of black caliper paint. Followed by a covering of ACF-50. Hopefully now it will now just need a yearly recover of ACF-50.

I suspect the task of the countersunk fastener mentioned is to stop the drum coming off with the wheel when it is removed, as it can be the case that they stick together in some circumstances. It is often the case that these countersunk fasteners are over tightened by those who associate their importance as requiring a high degree of torque, which some time later creates issues with their removal... I ever coat the threads with copperslip and just nip them up.
If you come across any really tight ones an impact driver and 2 lb hammer can do the trick.

I cleaned off the surface rust on my front discs and painted with hammerite smooth metal paint

Stainless fasteners into an ally casting almost invariably give issues after a few years. The ally corrodes, the products of corrosion are more bulky than the metal that has corroded, and to add to that aluminium oxide is a good abrasive. Not only are the threads much tighter than they used to be but they are filled with an abrasive powder giving extra friction.

Serious heat will sometimes work to expand the ally but often doesnt. The issue can be avoided in the fist place by coating the threads with Duralac or alternatively using zinc coated fasteners.

Boats having both lots of ally and lots of stainless fasteners give endless problems. But the CX series will have bolts into ally so beware.

I have some experience of stainless fixings and the impossibility of their removal from alloy after exposure to weathering, or worse still salt water, having maintained a sail boat for a few decades....However, when I typed of Kevin`s decision to utilise SS fasteners where possible on what at the time was his +8 is relative to the effect thereof after 20+ years, although perhaps only having covered a tad under 30k miles in that time, some of which was on salted roads with snow and ice around.

Bottom line, as I typed above the stainless fixings holding the steel tubular exhaust manifold to the alloy of my +8 head, having never been disturbed since Kevin had initially rebuilt the Mog 20 years previously, unscrewed without issue, which is a world away from my expectations relative to any and all exhaust fixings on my Porsche 991.1 at 10 years old and circa 43k miles...

The nuts and bolts Kevin chose to hold on my Mogs exh flanges together were also SS, and a couple or so years back when both two into one mild steel sections of the exhaust were past their best I was grateful for Kevin`s use of SS fixings which made replacing those two sections of exhaust so much easier...Such was the condition of the fixings I removed in the task, that I was happy to reuse them.

Kevin also utilised SS fixings to mount the wings, and some time back I also decided to unscrew a few of them to ensure that their removal and replacement would be a relatively simple process which it was, and I again re-used the same fixings. I think I posted a pic of the wing fixing and the surrounding area for those seeking to make comparisons with the look/effect of SS against their own wing fixings.

There are different grades of stainless steel and it is not suitable for all tasks as Howard has wisely pointed out

I am no metallurgist and type only of my personal experience relative to my +8, in the hope it might advantage any fellow owner.

I have spent a few decades struggling with the effects of corroded fixings, thus I also well appreciate just how rewarding and time saving and FAR simpler a task can be made, if one can put a spanner to a nut or bolt and it with a degree of confidence and to find that loosens off just as it should...

Just a quick update after checking the rear wheel area. In general most areas seem fairly well painted or plated. The only exceptions being the rear hub, which is unprotected steel and surprisingly the front differential carrier which is located above and at the front of the diff. The carrier is painted, but the finish was thin enough to have a lot of rust breakthrough on it, its also made of thin gauge tubing, so worth sticking some rust neutralizer onto it. The rear hub had a lot of rust build up under the alloy wheel rim, to the extent that it took a bit of effort to get the wheel off. Once off it cleaned up ok and is now painted to stop further issues.