Depends on the depth of the rebuild, if cases werent split and bearings, timing chain etc were not charged on your invoice, then it probably didnt get replaced. Here is the sticky thing, if the cases were split and they did not replace the seal, the cases pinch the seal a fair amount and cause indentions. If these 2 indentions (caused by where the case split meets) are not put back in the exact same spot, i could see it leaking. Did the seal you removed have the vertical lip that only come in the engines from yamaha, or was it the same as the seal you replaced it with?