Sorry I don't know how to assess your capacitor behavior. Mine was also weird as you may have read. I never did learn if those odd readings were due to my cheapo meter or what. Be careful !
Replacing the magnetron definitely solved my problem and she continues to work fine today 4+ years later. It was a bit of a chore since mine is over stove / under cabinets. I hope you have similar positive results. I think that's the culprit when you hear the loud buzzing - yes. G'luck, Ron