All cured.
I have installed the original gasket along with the new one as the profile of the new one was slightly diffetent. Although the gasket sealed the hole, as you can see from the below images the is a weak point in a channel which could provide a route in for air, unless torqued down massively.
Either way, the whistle is gone.
![[Linked Image]](https://www.tm-img.com/images/2022/08/04/DSC_0693.jpg)
![[Linked Image]](https://www.tm-img.com/images/2022/08/04/DSC_0694.jpg)