The real *** **** rarely (if ever) visits this site.
I've never heard of a water seal under primer. What makes for a good water seal would also prevent a strong bond between the primer and sealer. Though there are some good primers that stick to slick surfaces, these are intended for indoor use.
A quality primer and paint should be all the sealer you need.
Also, you don't want a sealer on the exterior. You want a paint that breathes so the excess moisture can escape. Latex shines here.
I'd remove as much of the oil primer as possible and use a quality latex primer.