Still no confirmed information but it seems clear that this is not a quick like for like exchange of the master cylinder, there is other development work still ongoing.

At least it shows they sre looking for a permanent fix rather than a quick one.

Because the new master cylinder is not a "like for like" substitution and may be from a different supplier the new part has to go through a re-homologation process so not to compromise the vehicles type approval. I'm told there are cylinders on test rigs in the factory going through test cycles 24/7. It is, I'm told, due to be finished this week.
Quite why this is needed when an owner can choose to change a master cylinder without reference to anyone, but the manufacturer cannot, beats me.

Peter, regarding your last point; I’m guessing it is because the parts will be supplied by MMC?

Bud
4/4 - Stanley

Warranty will be the big issue here as well, any adhoc fitment will void this for you instantly and your insurers would possibly step away also.

Is the problem one of a faulty batch that QA has picked up or simply poor initial selection and limited development/testing?
If the design is ok but faulty seals, manufacturing shortcomings then two options.
Ditch the supplier.
Get tighter QA in place with the supplier.
A third option is to have more than one supplier. Problems with one are covered by the second ( third even).
I guess that selecting parts for a car of known weight/ performance is fairly straight forward for stopping capability with space available to fit a second factor.
My plus8 had Austin Princess callipers. Off the shelf and suitable. Rocket science not needed.

The supplier is getting a lot of flack, but when it comes to rubber O rings the question is where we’re they sourced. Aviation has had this type of problem in that somehow cheap copies got into the supply chain. How that happened I don’t think was ever discovered, as the parts were supposedly ordered from the genuine manufacturer.
Think this type of problem is an on going problem as I see Russia is now trying to manufacture Boeing parts.

It is not the O rings. The brake piston housing is a porous casting

This mail arrived me at june 24.

"Dear Morgan customer,

We are writing to you with an update to the safety recall that is currently affecting your Morgan. We are sincerely sorry for the disruption that you have faced as a result of the stop drive safety recall affecting Morgan Plus Four and Plus Six vehicles. We are working tirelessly to identify a solution that meets the high standards of safety that we demand for our customers. Therefore, please rest assured that the necessary departments at Morgan are dedicated to getting you back on the road as quickly as possible.

We are pleased to report that we are close to validating a technical solution, along with the service action and vehicle movement process, and we aim to begin shipping the required parts to your Morgan dealer in the coming days. We cannot currently guarantee the date when your vehicle will be rectified, however we will keep your dealership updated with timings regularly, and they will be in touch with you at the earliest opportunity to arrange the necessary work required.

Once again, we regret any inconvenience caused by this action, our decisions have not been made lightly and we thank you for your continued patience and support.

Yours faithfully, "

and this from June 27.

"Dear Morgan customer,
We are writing to you with an update to the safety recall that is currently affecting your Morgan. We are sincerely sorry for the disruption that you have faced as a result of the stop drive safety recall affecting Morgan Plus Four and Plus Six vehicles. We are working tirelessly to identify a solution that meets the high standards of safety that we demand for our customers. Therefore, please rest assured that the necessary departments at Morgan are dedicated to getting you back on the road as quickly as possible.
We are pleased to report that we are close to validating a technical solution, along with the service action and vehicle movement process, and we aim to begin shipping the required parts to your Morgan dealer in the coming days. We cannot currently guarantee the date when your vehicle will be rectified, however we will keep your dealership updated with timings regularly, and they will be in touch with you at the earliest opportunity to arrange the necessary work required.
Once again, we regret any inconvenience caused by this action, our decisions have not been made lightly and we thank you for your continued patience and support.
Yours faithfully,
Morgan Motor Company "

Bye Marco

Correct:

This is an interesting read from the open university on the subject.
https://www.open.edu/openlearn/scie...ee-die-casting-active-atmosphere-casting

Clearly casting porosity is a known issue and some makers have a steel liner inside the casting.