I dont understand why after so many repeated attempts to inform them of your installer of the oil that this can not be made public or be information provided as asked.
Even under standard warranty clauses this is vital information.
Nissan has provided dedicated service centers to deal especially with this car and it is obvious that the installer does not want to be known, or you dont want them to be known. If in Martins position i would be hesitant also to accept what is simply being said without the information that was asked in close to the first response and subsequent responses about who the installer was.
After providing the information about the fluid needing to be shaken prior to him being able to contact the installer this could mean that the chain of evidence may very well be already corrupted. In the sense that the installer could now simply say he did shake it when in fact he may not have.
(The only informative text to identify the possible installer was something about Stewart's office)
It is pretty common knowledge that after the installation of every performance product something else is required to be changed to suit it.
Oil is a critical part of the gearboxes operation and if it is used to a different oil, obviously it would be a good thing to look into checking. I am surprised that anyone willing to touch the car did not run this past you given the sort of car that it is.
I think i am pointing out a few facts most are thinking.
I have read a lot on the standard oils in the colder parts causing the same issue as has already been pointed out. Which means it is not a Willall only problem, its across the board.
Who knows, you may have very well changed at a time (Winter) where the weather changes.
I am not saying that this is the issue here, but given the complexity of these cars, is it naive to maybe think it could be a possibility?
It seems like Willall want to help in any way they can though instead of seeking a resolution that would inform others when it was offered, the bashing continued. It is not about advising on a product issue as it happens with normal oil. In your case it just happen to start when you changed.
Given your attitude towards spending money for a service you have not received, if Nissan couldn't fix it, why did you pay them?