Help With Skylight Repair

[Dwightgibb]

We have a small leak in the lower corner of our skylight pane where the molding is separated about 1/8 inch.

I caulked it with latex, which worked for a week, but then failed - so it was apparently not waterproof

Is there a waterproof material which I can buy in small amounts for this sort of repair - I hate to buy a gallon of wet patch?

Thanks in advance.

Dwight