I have read the same about a NPD person. Those therapists who do try to treat it have a very low success rate. You just can't give someone something that they were born without.
Before reading and learning about MLC, I thought my H was a narcissist. In reading I realized that you don't just develop it later in life, that it was always present. My H didn't act like that until MLC hit. Sure he had flashes, but I believe we all have some tendencies. It's part of being human.
I believe the MLCer displays more tendencies of it during the crisis. They are all about themselves and don't seem to care who they hurt as long get what they want. I believe it's the selfishness that's the core of the damage that is done.
So, am I reading right that you believe your H was NPD right along?