thats the plate yup , look closely even a hint of a crack or anything strange REPLACE or scrap it , oil is ok .... no smoke or knocks ?? fill it with anything n flush it , i use a little diesel often and never had a problem , maybe 200ml with 400ml oil run it for 5 mins and drain . fill with fresh and if quiet ....... good to go but try another blade disc or bar with blades , see if your vibrations go away or even a bar with no blades.
blades look ok just a lot of use and well past useby
