Rear Differential/Gear Oil Leak

[jay02904]

So I had the rear final drive/gear oil changed out as part of a free service the dealer gave me (4 free services @ 600, 4000, 8000, 12000 miles) this was the 8,000 @ about 8,500 miles. Well I do the changes a couple times in between but they did the last one and i got the bike home the next morning i had a oil spot about the size of a quarter below the rear casing. i wiped it down, checked that the bolt was tight and no more spots on the floor but i have been able to swipe my finger across where the 2 "metal pieces meet" if that helps, no oil around drain bolt or fill cap just where the two separate "pieces" meet. do you think they filled it too much and if so the gaskets gone? or is this just residual...its been about 100 miles of riding since the change. should i just drain it and fill it the way i do and most others have suggested... I have changed it before but they way mac says on a 2x4. thanks