Why would the plastic in the timing assembly be such a concern for wear?
Unless there are huge alignment issues, the chain will not be wearing out any of the plastic. If it is wearing it out, you would have catastrophic problems to worry about, never mind the plastic. lol
Past BMWs: 2009 E93 335i -2010 E60 535i -2008 E60 M5 - 2013 M3 - 2008 E64 M6
Current BMWs:2015 M5 On Order July ED - 2014 F30 320i