Synthetic will not "cause" seal leaks. That myth got started when high mileage engines were changed over from conventional oil to synthetic. What happens in that case is that there was already a leak present, but was being masked/stopped by varnish buildup in the seal. Synthetic oil tends to very high detergent, which will clean the varnish out of the seals, which made the leaks show up.
You won't have any problems running synthetic, but you may want to wait until you get some more run time on the engine so that is properly broken in.
