It gets done each time I get it serviced of course!, a friend of mine hasn't had his Merc's oil changed in over 38,000 miles, the performance is only slightly down, silicon based "oils" have about five times the life of the old type, I remember using Redex regularly many years ago, & choked near neighbours with the black smoke it generated, you had to rev the engine for about three minutes, I was popular, they all rushed to get their washing in, oops!!