I second the notion for upgrading to new Beckson ports - my only complaint is that they don't have an internal ring to support a port bag - but they are a much more solid and water-tight improvement over the Viking Marine or other ports I've seen.
When bedding in a new port ring, be sure to drill all holes, goop up the deck and the port with sealant, install the port loosely with only two screws opposite each other ON the highpoint of the deck curvature (if any), let the goop setup at least overnight, then apply the rest of the screws with light to moderate tightness - plastic screws are much better for this application too (though I used stainless in the picture below). The key to a good tight port seal is to not distort the port base by cranking it to a curved deck. Let the sealant do the work of making up any difference between the curve of the deck and the port. Now your port threads and o-ring will be nicely aligned and mostly jam free.
Also note that 3M 5200 cleans up beautifully with Mineral Spirits before it's cured - that's how I finished the sealant around the edge of these port covers.