Problem with Royal Palm?

We've had this Royal Palm for about 4 years now. It went thru a couple of very hard winters, but with the recent past mild winter and this beautiful summer we are having, it's really looking good! EXCEPT, the trunk is cracking on the north side (only one side of the palm). We have another royal in the back of the house and it is also cracking a little on the north side. Is this normal? Anything to be concerned about? Pics below.

P.S. - I haven't been on Dave's in quite a while and LOVE the new addition of the multiple image upload!

Here are some pics of one of our other royals in the backyard. The cracking is not as severe on this palm. Again, it seems to be only on one side of the tree (facing approximately north).

The clothesline is a temporary and is not tight on the tree.

cracking of trunks is sometimes blamed for excessive moisture when the conditions are not great (too cold usually)... or if palm is grown in a swamp, or in mud. We don't get that look much here in So Cal since there almost never is too much water.

Thanks, Palmbob! Right after we put these royals in, we experienced two very hard winters with temps below freezing for extended periods of time. I usually don't water a lot... not even as much as the county will let me, but I might have during the cold temps (can't remember). Could the cold temps alone have caused this stress? Also, will this hurt the tree? I have a desire to get some mudding compound and fill in the cracks! LOL

it opens the tree up to insect invaders, but otherwise should not hurt the tree too much (though once tall it may reduce the amount of lateral stress the tree can tolerate- in other words, a strong wind could snap it in half)

Is there anything I can fill the cracks with??

maybe plastic wood (a common wood repair glue), but I have no idea if that would really help

Thanks! Appreciate the reply!