Had the same problem when we bought our 95 Catalina 30. This fix assumes the seals aren't broken or torn.
First clean the rubber and the portlight with a paper towel soaked in water and dish detergent. Once you've got them clean, get a small jar of vaseline and gently work it into the seals. Really work it in with your fingers, I spent a good ten minutes per port.
When you're done, wipe them down with a clean paper towel to remove any excess and leave the ports open for a while. The seals will swell a bit. Close the ports and dog them down and they should seal now.
I did ours in '08 and they still don't drip unless it's blowing a 'nor 'easter.
Hope this helps,
95 Catalina 30 Island Time
“Only two sailors, in my experience, never ran aground. One never left port and the other was an atrocious liar" - Don Bamford