Agree with others, walnut. Occasional use of Techron cleaner (every 3k miles) is also beneficial imho.
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Enjoy the Drive,
Steven
2014 435i M-Opt, M LSD, Dinan CAI/IC/BTurbo/Stage 4, ER TIC/CP, GFB DV+, Fabspeed HJS cat DP & Mich PS4S.
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