There is a similar discussion going on about locking the center diff on a GST.
While it's a good idea to lock your center on a MT that is going to be bashed almost exclusively, I have to strongly suggest not locking it on a truggy, which is a track vehicle. Of course that doesn't mean you can't bash it, and if that is what you want to do with it, lock it and do some wheelies. However, I will say it again. On a track you want control and you will give some of that control up by locking the center.

About the weight of the oil... A guy in my club just got a CEN Matrix Arena Pro and a CEN rep told him to use something weird in one of the diffs. I think it was some automotive gear oil. Can't quite remember, but it seems to work very nicely. I will find out what exactly it was and which diff he put it in.