As you can read in those links the Redline "Heavy Shockproof" is not for use where there is synchro engagement. ie gearboxes and exotic diff setups. Heavy is OK to use in normal crown, pinion and gear operation like our transfers and rear diffs. In fact Heavy is often used in old school competition EVO I-III rear mech diffs to make them bite and engage more harshly. Just keep the Heavy out of your gearbox and its Ok to use. Plus if you ever decide to change from Heavy to something else, clean the internals as best you can to get rid of the snot, because thats exactly what it looks and feels like when it clumps together inside your diff lol. I hate cleaning it up because it feels like artificial snot and it has to be wiped off to get it off parts as a simple parts wash in diesel etc wont get it off lol.