You can find on Ebay a complete MBX6 center diff, which fit perfectly in the 5.
It's lighter and the teeth shape on the spur is different. I tried it yesterday and I can ajust the mesh very tight without any noise
It's true that the mbx5 spur make some noise, so I think it's a good solution to get the lighter mbx6 diff.
I am almost sure that the rear and front diff spur and bevel are the same between the mbx5T and the mbx6T, to be confirmed by other...