I have not figured out how to get this to work.  I'm trying to doing this on a stereo track in comp mode where the split point has the automatic fades inserted.  The project was saved this way.  If I do automatic comp select it works at split point but creates a new split point where I let go??  I guess the work-around would be select all the way back to the start of the clip.  I also have trouble with the fade tool popping up, when I want the comp tool, when tring to get near the end of a clip.  Just saying.
 
The manual states:
 
You can also manually heal abutting healable clips. To do so, select the clips, then hold down the CTRL key and clip one of the selected clips.
 
Thanks to all the great folks here on the cw forum!!!

kzmaierIf I do automatic comp select it works at split point but creates a new split point where I let go??  I guess the work-around would be select all the way back to the start of the clip.

I wouldn't call this a workaround. It is precisely how the feature is intended to work
 

kzmaierI also have trouble with the fade tool popping up, when I want the comp tool, when tring to get near the end of a clip.  

 
Not sure what the "trouble" is.  Do you know the "fade tool" as you called it (actually called cross comp too, I believe) also allows you to move the location of the split and crossfade?  This is a very flexible tool for comping.  Is it doing something you don't like?
 

kzmaierYou can also manually heal abutting healable clips. To do so, select the clips, then hold down the CTRL key and clip one of the selected clips.

 
This works.  What is not explicit in the manual is that once the clips are selected, you need to bring the cursor down to the lower portion of the clips to activate the comping tool.  Then CTRL + click will heal them.

neirbod
 
This works.  What is not explicit in the manual is that once the clips are selected, you need to bring the cursor down to the lower portion of the clips to activate the comping tool.  Then CTRL + click will heal them.

^^^^ I think this is key to the subject line - "comping" is done on the lower portion of the clips.  So you have to drag along there to heal, since the heal command is part of comping.   The upper portion is for typical track level behavior - select, slip-edit, etc.   
 
I also just learned last week that there's a dedicated Comp mode...   See the section "Comping with the Smart tool and Comping tool" here:
http://www.cakewalk.com/Documentation/default.aspx?Doc=SONAR%20X3&Lang=EN&Req=Arranging.45.html
 

Thanks neirbod,
 
This is what I was missing!!!
 
What is not explicit in the manual is that once the clips are selected, you need to bring the cursor down to the lower portion of the clips to activate the comping tool.  Then CTRL + click will heal them.