Maxwell windlass VC500 maintainence oil

[captran]

I did a search on the message board and came up empty on this question.  The manual says Shell Omala 320 or Castrol SP320 or equivilant gear oil.  Don't often use my windlass but thinking it's overdue for changing out the oil.  I see places on line that sell 5 gallons of the Shell product.  Anyone in the NW have a source for gear oil and a preference?  thanks