the seal has now been replaced FOUR (yes FOUR times) over seven days - it leaks overnight while the car is just sitting on the workshop floor !
I am by no means a mechanic or engineer, but to me that sounds like either staggering incompetence in the dealership service department (and I doubt that is the case to be honest), or there is a very unusual flaw in the way the two metal surfaces contact the seal.
My money would be on the new engine.
I should add my 2015 GT developed an oil leak that had wisps of smoke coming up from under the bonnet. Called the dealer who seemed familiar with the issue. Car taken to service the following day and fixed first go. It has been 2 years and no further oil dramas thankfully.