"In most cases a visual inspec
"In most cases a visual inspection will tell you. Unless they have been frozen, the leak is usually at the mating surface at the riser. By removing the riser you can inspect the surface of both the manifold and the riser. If you want to be sure, you can remount the riser using a closed system block-off plate and fresh gaskets. Plumb a radiator pressure tester to the cooling line and make sure there are no other hoses or fittings open, such as drains, shaft seal hoses etc. Pressurize the manifold and spray it with a soap solution. You should also monitor the guage for leakdown since a leak into a port may not be visible. If the guage hasn't moved in say...an hour, you're good to go. That doesn't speak for the riser, just the manifold. If the riser looks questionable, or is over 5 years old (less in salt), just replace it.
Rick"