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Hey Guys...
I'm going to replace the oil in the diff and gearbox of my 2001 6-speed.
What should I use in the diff?
What should I use in the gearbox?
What is the best for smoothing out the notchy gearbox??
Any advice is appreciated.

Wrong Forum.

I tried Penrite Sin 75 originally in my 6 speed and found it got notchier and notchier. Got to the point I was worried I was actually losing syncho's so I dropped it out after 3000k's and put in Redline lightweight shockproof. Massive difference but it was $135 for the 3.875 litre bottle. I put royal purple max-gear 75-90W in the diff but that's a Clutch pack diff. On the open diff I just used penrite ten tenth's and that was fine. Came out very clean when I swapped diff centres. Not metal shaving, though again..3000k's on that oil.

how often should gearbox and diff fluid be changed?