[Opie55]

As a trial lawyer, I would advise you to go outside and scream and swear for a few minutes, then move on with your life. You won't find mistakes in questioning a mechanic on the stand cold. There are not going to be common oil filter housing mistakes. As to whether he saw metal fragments when draining the oil, not if he drained it directly to a big tank like many places have. No question the mechanic is a bad mechanic based on the idiotic starter suggestion, but the odds you win this are not good.

EDIT: And I should add that since you traded in the car you now have no physical evidence. You cannot even show what happened to the engine internally, which would be step one in proving some other thing caused it. You really have no case at all.