[macojoe]

Well there must be some soft floor there to cause flex to make them get wider.

There is no easy fix if you want o do it right!!

First thing is to check deck for soft spots. Repair as needed.

Second you need to take a dermel and V out the cracks, at this point you would glass and sand to fill the void.
Then sand and paint.

Could try to fill with F 27 but that just fills the crack, if there is flexing in the deck and the crack gets wider it would last long.

Good Luck!