If you haven't done or aren't doing them regular your best bet is to get yourself a suitable dial indicator and a magnetic stand for it.

The factory specs are pretty precise and the ability of the average wrench to determine if an installation is definatively within the specs is a serious challenge.

Doesn't cost much to alter the wheel bearing to what might be a better position but you've mentioned the vehicle is older and might be sitting on its original suspension parts. It might be worth it to get the car up on a lift and give the suspension a good going over before you start spending too much on any particular part/s. There are more that a few places that the front suspension can be worn and loose contributing to a sloppy steering feel.

Best advice is to access a Factory Service Manual which Mercedes at one point made available on line. That way you can get a basic idea of where you're going with addressing these kind of issues.