determine type of rear end

I bought my 2007 Tacoma Double cab 4X4 used, want to change the differential fluids,how can I determine if the rear is limited slip and if so do I need to add an additive?

 

There would be a sticker by the fill port.

If in doubt, any Toyota dealer could tell you if it was originally equipped with an LSD by looking up the truck by its VIN.

Or, jack up the rear axle, put it on jack stands, and with the transmission in Neutral and the parking brake off, turn one wheel. If the opposite wheel turns the same direction, you have limited slip. If it turns backwards, you don't.