The diff cover has now been used in ny 511 for approx 20 full battery runs during both dusty and wet conditions.
After one the racing sessions the car looked like this
http://www.tamiyaclub.com/picturefra...09222743_7.jpg
This is how the pulley looks:
http://www.tamiyaclub.com/picturefra...09222743_8.jpg
And on the inside:
http://www.tamiyaclub.com/picturefra...09222743_9.jpg
Note that I also use a protective seal. This of course helps to keep the diff clean on the inside.
I´ve also made the diff cover compatible with a reversed damper setup:
http://www.tamiyaclub.com/picturefra...09222743_1.jpg
You simply flip a part of the upper cover and Vóila!
I´m in the final stage with the 501X cover. I expect to have it ready next week.
Same goes for the lipo solution for the 511.