Thanks for the response. I'm going to keep using one or the other.

But Billman has a point too...I know a number of people [mostly who live in New England where the temps get below the 20 degrees F we can get around here] who use Mobil1 75W90 and haven't had any problems.

 

Ever since I bought my S2000 and joined this site, there has always been a controversy as to which diff oil to use in the S2000. I think Road Rage did a good job of trying to explain why Honda recommended SAE 90 to us, but here is an article that may help us understand why this viscosity was picked and also illustrates the gear oil J306 specs. You have to also remember that we only use 0.78 quarts of oil in our differential to do a very tough job.

http://www.lubrizol.com/products/automotiv...ar-oil/J306.asp