The center diff with 2m oil wasn't as bad as I expected, it only diffed out when it was nearly vertical. Mine was leaking terribly, one of the screw holes stripped out and I couldn't cinch it together properly. Did ok in testing, but by the time I got the to trail, it wasn't nearly as stiff. I rebuilt it with an aluminum case and it's holding together now, but didn't re-install it.
For crawling around, I found a locked front, center, and open rear worked the best for me. Locked rear tended to push it off line on serious climbs - letting it slip a bit helped calm it down. I think if you have a bit of speed, open front and rear would do fine for trailing around and occasional crawling and take a lot of stress off the driveshafts. The silicone earplugs worked great for me - still allow a little slip, but not much. If you crammed them (or 2M oil) in the diffs, it would do pretty good I would think.
I'm thinking about using silicone in one of my TRX4 Sports and doing some experimenting. Not sure if it will have the same effects or not - I think its more of a function of a rear motor IS chassis than anything else.