My Breaker Box Is Possessed!

After having a problem on one circuit in the house with a sizzling sound from the box and lights flickering, an electrician replaced a breaker and all was well - for about a week. I then replaced the same 20 amp breaker with the problem coming back. I noticed that both, the 20 amp and 50 amp breakers on the same post of the bus bar were burnt. I lightly sanded the post, applied electrical jelly, and replaced the breakers. And, the problem came back.

I shut off the 50 amp breaker and the problem continued in the 20 amp. I have no other problems on this bus bar or in the house. Will replacing the bus bar cure this or should I look elsewhere?