When new fork seals leak it's usually because they incur micro-tears as they travel down the stanchion tubes on the way to their destination.
Even on new stanchions it is advisable to slide them into place using a bit of plastic wrap or a baggie with a hole in it. A little lube won't hurt. Once the seals get to their destination, gently pull out the prophylactic plastic.
Fork seals give me between 20 and 30,000 miles service when installed this way.