Why is the inside of my rabbit vibrator turning brown?

I only bought my rabbit wave vibrator two months ago, and after the second use I started noticing that the inside of the shaft part began turning brown (it's really supposed to be pink/clear) -- the second time I also submerged it in water, but it's waterproof and I didn't have any issues. I did leave the batteries inside the first two times, so I thought that most likely it was my own fault and the batteries were eroding/leaking inside of it. when i opened the battery compartment to remove the batteries, there was no brown liquid and the compartment/batteries were both completely dry. i've washed it with soap and water, but the brown liquid/stain is definitely inside (mainly on the motorized parts). any ideas what this is? (and i knoooow...i'm going to have to buy a new one :'-( and I definitely will NOT be buying another pink one)