I have to buy the knob and shaft, correct? I want to replace the original with a zebra wood so that it will match the other wood in my car. It's $70 including the shaft. I can also get just the wood knob for $40, but it says "Professional installation recommended." I take it I can't just replace the knob myself? By the way, it's a 1992 190E. I would appreciate any advice on this topic. Thanks.