How do I know if it's the spider bracket or the bearing? Do I have to take it apart? Thanks.

You might need to elaborate a little bit more as none of us are there with you and can't read minds either. What are you working on?

Very likely it's both. There is a design defect in the spider bracket because it is made of aluminum and the tub is made of stainless steel. This causes electrolysis like a battery where the more reactive metal, aluminum, corrodes away rapidly. Here are some metals with a saying to remember their order from most reactive to least:
potassium = please
sodium = send
lithium = little
calcium = charlie's
magnesium = monkeys
aluminum =and
zinc = zebras
iron =in
lead =lead
copper =cages
silver =securely
gold =guarded.

Read more: http://wiki.answers.com/Q/A_list_of_metals_in_order_of_how_reactive_they_are #ixzz1ns8Y5ftf
As you can see aluminum is above iron, but stainless is a mixture of iron, nickel,and chromium, all less reactive than aluminum. If you put both metals in soapy water you will get current flow from each end. The only way to prevent the corrosion is to attach magnesium to the spider gear as a sacrificial metal.