RCknight,
I can promise you Corally diff's don't last longer they are open, the xray diffs are sealed so they last forever but the Corally diff is good for about 5 runs
on my tc4 i use the steel spool and the plastic diff i put black grease on the cvd pins for both the spool and the diff this works well for me since my diff has 15 runs on it and it is fine