Variable text field in root cannot reside in a movie clip?

I have a movie clip ("mod_control") that resides within other clips that determines the name of its parent and adds a number to a corresponding text field when they appear on stage (example: "Widget_1_count", "Widget_2_count", etc...)

Using this code in the clip works fine:

// get the parent name, example: "Widget_1"

var this_part = Object(this).parent.name;

// get the current value in the corresponding text field, example: "Widget_1_count"

var c_this_part:Number = Number(Object(root[this_part + "_count"]).text);

// add 1 to the current text field value

var v_this_part:Number = Number(c_this_part+1);

// update the text field with the new value

Object(root[this_part + "_count"]).text = String(v_this_part)

I will eventually have several dozen text fields (for several dozen parts) so I now contain them all in a movieclip with instance name "part_count".

So I added part_count into the target path:

var this_part = Object(this).parent.name;

var c_this_part:Number = Number(Object(root.part_count[this_part + "_count"]).text);

var v_this_part:Number = Number(c_this_part+1);

Object(root.part_count[this_part + "_count"]).text = String(v_this_part)

...but that produced this error:

and then I tried this:

var this_part = Object(this).parent.name;

var c_this_part:Number = Number(Object(root[part_count.this_part + "_count"]).text);

var v_this_part:Number = Number(c_this_part+1);

Object(root[part_count.this_part + "_count"]).text = String(v_this_part)

...but that produced this error:

As is often the case, I may have overlooked an obvious nuance of syntax... could that be the situation here, or is this action simply impossible in flash?

I appreciate the wealth of knowledge and experience here and thank you in advance for giving my issue some thought.