Hey folks,
Came across this thread and thought I'd offer a few inside tips:
1. Do NOT try replacing the fluid with anything other than Valvoline Invaritorc 638. NuVinci customer service should be able to hook you up. It truly is a special fluid. Almost everything else will slip.
2. Without better pics of your parts, I can't tell for sure but it is very, very likely that the failure you experienced was the freewheel, not the trans internals or the fluid. When the fluid is failed, it looks like gray jello, and it takes quite a lot to fail it. In fact, it will never fail under even the most extreme human powered bike use that it was intended for. When this happens, there are usually accompanying severe score marks on the rings, balls and/or central idler. I don't see any of that in your pics, in fact, the traction surfaces look great.
3. The other possible failure point are the tabs on the input driver. I didn't look at your engine specs, but I would guess that the power is well beyond what the bicycle design levels were and the spikes from combustion events can pound those little tabs right off. Some sort of torsional isolator, like a rubber coupling, would do wonders for life if this is the issue.
4. One last possible issue would be that the cover was already coming unscrewed. This is the least likely possibility and usually only happens under high, repeated, REVERSE braking loads. The cover torque spec is ~300 N-m, and Loc-tite is used on it.
5. You don't want to add any shims to the unit. This will just make it hard to shift. If there is enough wear to require more shimming, it would be very, very visible on the balls and rings.
With respect to the missing cam rollers, that would mark this unit as a bike production hub. The hub that comes in the NuVinci Developer's Kit has a full complement of rollers, along with some other tweaks, to make it more durable in high power apps like yours. The Developers Kit also has a programmable automatic shifter that you can set up to hold either your engine or your pedals at a constant rpm.
Hope this was helpful!