when I got my tires changed couple days ago ,I found that there is oil/(may be some liquid) on the surface of the differential . Is that considered as oil leaking ? wht should i do pls ?
thnks!

 

You need to determine what kind of fluid it is. Wipe off some and smell it. If it smells like rotton eggs (or a bad fart), then it's diff fluid that has found its way out of the casing. Now you have to figure out from where and fix that.
If it's sorta reddish and doesn't smell too bad, then it's likely one of the fluid filled diff mounts is leaking. If this is the case, replace both.