Is a leaking manifold freeze damage?

Often. Skipping or rushing a fall blowout is the most common cause of cracked manifolds.

Valve box full of water: what it means

Some water in a valve box after rain is normal. Water that refills after you bail it out, or a box that's full in dry weather, points to a leak.

Bail the box out on a dry day with the system off. If it refills, the leak is upstream of the valves — often the manifold or a fitting.

Leaks usually come from:

Is a leaking manifold freeze damage?: Often. Skipping or rushing a fall blowout is the most common cause of cracked manifolds.