I use plain old regular Mobil ATF which I get at my local Costco. It's about a dollar a quart and seems to work great. I figure I'll just drain and fill the trans once a year and change the filter every other year. I really don't think there's a substitute for frequent fluid changes. In the diff. I use Mobil1 like a lot of others out there. Someone posted pictures of what theif diff. looked like inside after using Mobil1 and it was pretty amazing. It's expensive but since you only need one or two containers, it's not so bad.

I have heard great things about Redline and Amsoil oils and I have no doubt that they're better, but again, frequent changes, I think, are the best protection.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside