at / on my part

[Mnemon]

a. I was racked with guilt on my part in making her this unhappy.
b. I was racked with guilt at my part in making her this unhappy.

Both correct?

 

[Piscean]

a. I was racked with guilt on my part in making her this unhappy.
b. I was racked with guilt at my part in making her this unhappy.

Are both correct?

At my part is incorrect. On my part is redundant.

 

[Mnemon]

At my part is incorrect. On my part is redundant.

It's Aalways nice knowing your ideas about different matters, Piscean. Thanks. (edited)

 

[PeterCW]

At my part is incorrect. On my part is redundant.

"At my part" would be used if you were one of a number of people who had contributed to her unhappiness. If you are the sole cause of her unhappiness then I would agree with Piscean

 

[jutfrank]

I think the question should be which of several prepositions is the winning preposition in this context. I vote for for.

I was racked with guilt for my part in making her this unhappy.

Second place goes to over.