Thanks. I don't own one yet, but I've been seriously considering one of two CPO 328is. I'll definitely be checking under the filler cap before committing to anything. I've read a few posts indicating all of the chain guides start white and darken over time. Are you sure the guide in that first picture isn't just darker because it's older? In this BMW N20 production video from 2012, the chain guides that are installed are white (go to 1:30 into the video).
I also noticed on RealOEM that the chain tensioner part number never changed; only the timing chain part number.