Teak Deck: sealing joint to skirting board

My teak side decks were new-laid in 2009 (glued, not screwed down). I cannot remember with certainty now, but the skirting plank along the bottom of the house sides may or may not have been replaced. In any event, instead of a caulking line between deck board and skirting some other filler was used. In 90% of the length around the house, the skirting/deck joint is tight....but there is a section where a gap has opened up. In the photos you can see the tight joint (top left) ...and the other two (2) photos show a gap, with the now cracking filler just visible. (You will need to click on the photos to enlarge, sorry.) Moisture accumulates along this gap line...and I don't like/want that.

I am looking for suggestions on how to fix this. Taking the skirting plank off right-around, putting in a black caulking line and re-fixing it would be a lot of work I think. Is there a filler I could consider using just in the length that has a gap opened up which would be unobtrusive/inoffensive?

The plank abutting the house does look different, and the gap width between it and second plank inconsistent in width. My decks were redone in 2012 and involved all planks. Perhaps the variable gap took up any inconsistency where the new planking finished.
In my research years ago I discovered TDS products which are specific to deck work. I also discovered the need to have the caulk not attach at the bottom of the "groove". But, as you need to rework a small area you could use Sikaflex (?291, they make several versions),readily available at Bunnings. Remove the old decaying caulk with a fine scraper like a narrow bent tip screwdriver, tape the edges,and fill. You might need to sand afterwards to flat.
I remember searching online and finding videos of how to do it,and pages of illustrated instructions. But you might not need to overthink what I hope is a small job. Though it could recur as other areas fail.

I just saw this post, why not get the TDS guy to deal with this issue when he does the bow section? http://www.trawlerforum.com/forums/newreply.php?do=newreply&p=703686