Q. 8 months ago, my wife was cooking chicken for Shabbos. The food was being cooked in a cooking dish, made out of stoneware with the exterior made out of enamel.
In the dish was a few pieces of chicken, rice, water, Italian dressing, salt, spices, and a little bit of balsamic vinegar. The problem is that after we cooked and ate the food, we realized that the balsamic vinegar did not have a hechsher. The balsamic vinegar was made out of wine and grape must.
There certainly was 60 times heter per the amount of balsamic vinegar that was put into the dish. However, there is a concern of Avida Leta’ma as the balsamic vinegar was put into the dish to add flavor. I do not recall if the vinegar was discernible while eating the chicken, as i was not paying attention being that at the time I did not think that there was a kashrus issue.
In terms of hefsid merubah, the price of the dish is $50. 
Please let me know what the teshuvah is.

A. Horav Shlomo Miller’s Shlit’a opinion is that since the balsamic vinegar is at worst a derabbanan prohibition and it is not the only flavouring item present (ze veze gorem) the cooking dish could be kashered by boiling water three times over the fire.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a