In the easy-to-clean category MS Natural wins easily. I never used the 4000 but my Elite (still work after more than 20 years) can be washed in the dishwasher.
I washed one of my Natural in the dishwasher, and it still worked for a while, but as hard as I tried to make sure it dried afterward, the keys started to feel more "scratchy." It's possible this would all be in my head, but I feel like the water did do some level of damage.
It might be the heat you ran the wash at, what temp/setting was it?