I am wondering how we pasken when only part of a kli was hit with issur, for example, I had hot milk boiling in a milk frother that was sitting on top of a fleishig microwave (in retrospect probably not the best place for it). [The microwave was ben yomo.] the milk overflowed and fell into the microwave while it was still quite hot – it hit the inside of the microwave door and part of the floor of the microwave. I’m assuming I can do hagalah on the spot where the milk hit, but I’m wondering do I have to kasher the entire microwave or just the spot where the milk hit?
In this instance you can just do the part that was hit.