For cases 1 and 2, the indefinite article fits best.
For case 3, either is possible. The use of "the tendency to curse", with a definite article, would mean that the speaker thinks such a tendency is an established thing that they can point to with "the".
But the indefinite article is more likely even in example 3.
The examples have nouns modified by preposition phrases and "to curse', but that doesn't determine what kind of article to use.
The OP has mentioned a reference that says that post-modification calls for a definite article. Here are two examples of post-modification by clauses:
This is the time of crisis that we were warned about.
That example requires a definite article because the thing referred to already exists in the speaker's frame of reference.
This is a time of crisis that we must respond to.
This second example requires an indefinite article because it refers to something the speaker introduced at that moment.