Filling cracks in Mahogany

[sportin_wood]

It's that time again to remove/refinish the varnish on my mahogany rails. Some of the joints have come loose and have an 1/16th to 1/8th inch gap between them.

I used some wood filler (mahogany color) the last time I revarnished. The wood filler (elmer brand I believe) cracked under the finish as my skiff takes a good beating out on the ocean 100+ days a year. Is there anything more durable?

What do you guys usually use to fill underneath the varnish?

Thanks, Jason
http://members.cox.net/jhaya/images/1stcoat/MVC-002F.JPG

[Al Thomason]

I use BoatLife caulk between the gaps on my cap rails (Black), and have also use some left over 3M Black Teak or 2-part deck caulking.

I am not using Varnish over them and do not know if there would be any issues with adhesion.. (I save my varnish work for interiors and use Cetal on the external bright work)

-al-