hi, there
1) Oil filter can be purchased from repco. Its model is 2664P and should cost you about $32 (Lexus will sell it for a few folds). Both the Lexus and repco ones are similar in that they are made out of some sort of paper material which you replace at each oil change
2) IS 250 takes up 6.5 litres of 5w30 oil.
Not sure if Lexus dealers put in fully synthetic (as I have enquired with the service rep and it's either he was clueless or did not want to disclose anything) but ours runs on mobil 1 fully synthetic oil.
For our recent service (our IS250 just passed its warranty period), I brought the car to my regular performance shop (that is known for thorough workmanship on performance cars) . Car runs as smooth as ever and the cost was about 60% of what Lexus charges.
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