I can't find SAE90 hypoid oil for my differential at any auto parts stores. Why? Is this typical?

 

Yes, and your Dealer has it is a 55gal drum if he has it at all.

Here is a link the the FAQ on the under the hood forum.
Differential fluid change:

 

I found 75W90 gear oil at pep boys no problem; according to xviper's thread this is fine to use. Hasn't caused me any problems since I changed it ~2000 miles ago.

 

advance auto parts has mobil 175w90

 

Amsoil makes an 80w90. For extreme shock loading situations (you do clutch drops), you could mix equal amounts of 75w90 and 75w140 and get a 75w115.

I found a straight 90wt a while back, but nobody seems to have used it, and a straight 90w is an odd recommendation since almost no one carries it. In very cold weather applications, 90 weight will not adequately splash for many minutes of operation, which will suck power and fuel mileage, and reduce the efficacy of the lubricant.

Any of the "Honda engineers know what they are doing" fans going to explain this apparent oversight? XViper has published a Canadian TSB that recommended 80w90, but apparently that was done to quell the gut churn that Honda's retarded recommendation was causing in people such as yourself. The 2004 Manual still says 90w, and why would Canada be unique? They get the same parts, and while it is typically colder there, there are many spots in the US (Minnesota, Wisconsin, N. Dakota) where it gets flat-out cold.

 

From National Weather Service:
[QUOTE]
PUBLIC INFORAMTION STATEMENT
NATIONAL WEATHER SERVICE DULUTH MN
845 AM CST THU JAN 29 2004

[snip]

OTHER LOW TEMPERATURES:

MINNESOTA

 

Yes, I have been using 85w 90 and changed the fluid at a much earlier interval than what the manual recommends. Thanks for the info.