I am in a Penrite phase at the moment, so used HPR5 5w-40 in mine, which is working well.
I'm sure the Motul will be equally up to the job.

As far as a flush goes, I have never tried anything.
I just drain and put in the new oil for my first change, and then change a bit sooner for the second change.
Then back to a normal interval for the next change.