[C320-list] Leak in fixed lightports in head

[kspir4 at cox.net]

Hi Folks,
Yikes---- I have a leak around the two fixed light ports in the head.  
1.  I may need to redo the seal around the window.  If so, is there any guidance on how to do that?  I searched our website and found lots of suggestions regarding leaks around opening ports but little about the fixed light ports.  I did find and view the Boatworks Today on Youtube that shows how it install the glass with butyl tape underneath and caulking on the sides ( https://www.youtube.com/watch?v=MQyjxVUskd8 ).  Is this the recommended process for 320s?  Also, are there recommendations on how to remove the old window and where to purchase the new one (assuming the old one is pretty much banged up during removal).
2.  On close investigation, I can see (from the inside of the head) what appears to be cracks along the edge of the bulkhead "frame" that the window is set on/ in.  The cracks go around about 60% of the opening diameter and appear about halfway between the approximate 1/4 inch distance between the glass and the inside edge of the head's bulkhead.  The water is DEFINATELY coming in through these cracks.  My question is:  is this where a sealant failure would allow water to enter the boat OR might the sealant be fine and the cracks be a structural issue that is allowing water to enter from another area that is compromised (for example:  a leak around the sliding hatch door or other cabin top opening).
 
When I get to the boat this weekend, I am going to try to isolate the source of the leak by spraying water only in the area of the glass to see if water appears on the inside.  If water doesn't get in, I'll spray other parts of the cabin top to see if water gets in from somewhere else.

Until then, I thought I'd ask if anyone has any other suggestions or experiences that may help?  
Thanks in advance!!
Ken Spiro
MoonDancer
2006 / 1089