I am an amsoil fan and use it exclusively in my vehicles. Thats only a preference. However for manual transmissions, you need to find out your transmission requirements. A transmission that requires GL-4 should only receive GL-4 and not a general GL-4,5 oil. It will destroy the yellow metals regardless of what the manufacturer states for it having a general compatibility. From experience, I destroyed my transmission in my nissan by using a "GL-4,5" compatible oil from royal purple. I now only use Amsoil GL-4 transmission oil and have had no problems. But there are other suitable GL-4 oils out there, its just a preference.

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airedale2 Welcome to Texas
1984 MB 300D 266,000
1993 Nissan PU 271,000
2002 Tahoe 122,000
2004 VW TDI 75,000