My 2008 Z4 is taking longer to start. It turns over, but takes a few more seconds than usual and the time seems to be increasing. Seems like the problem is with the starter? My question is, should I replace it before it goes out completely? Not sure how long it has left and don't want to be stranded. I'd like to have time to order the part before I take it to the mechanic. Would it be the starter motor or the ignition?