diff q newbi

I dont know if my diff has a leak or if it is just coming out of the vent that is why i need to know if the vent is at the top of the diff becuse i drove it hard last night and left some cardbord under her last night and saw nothing but then today i put her on the lift and saw a trail of oil from the top of the diff i need to know if that is just blow out from the vent. I think i am just going to put some rp 75w140 and see if that helps any info on where the vent for the diff is would help also if anyone has had this what did u do for the fix