Is gear oil... gear oil?

In my quest to get my boat ready for storage, I went down to the local
X-Mart for lower unil gear oil (grease?) They had only 2 quarts of Marine
80W90 GL5 gear oil, and I bought both quarts. Not knowing if this would be
enough to refill the lower unit, I went across the street to Advance Auto
and purchased a gallon of the same stuff... but it wasn't labeled as marine.

I know now that my gearcase only holds 22oz, so I kinda bought way too much.
But if it's the same stuff, I'm not too worried because it shouldn't go bad.
Anyone know if it has to be labelled for marine use, or is there a
difference in 80W90 GL5 grease???

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