I agree with the others. Change the 90W a couple of times a couple of days apart, and run it unless there's a noise. Check for a bad boot over the shifter, as mentioned.

Toy t-cases are stupid simple and unless a bearing is full of play or roaring, it's probably fine.

FYI, any time you submerge a toy above the top of the t-case for very long, you need to check the fluids in the tranny and t-case. They're not sealed and they vent though the shifter tower. So it's not hard for water to find a way in.