Thanks for all the input guys. I have a few weeks to "try" before I buy and I have to say there are some things I now understand.
Its a 42 not an S/42.
It has a military barrelproof mark.
It does not have a letter in the serial # (so maybe its a first run or last run in the series?)
While the Luger has a rep for being "finicky" I was suprised at how robust the action is. The steel is heavy and the gun is solidly built. And talk about a magazine that is HARD to load.
I know also understand the origin of the 9mm vs 45 argument. When loaded a luger and a 1911 weigh about the same. The luger can't feed hollowpoints and in over all size the luger is THICKER and the sights are tiny. The luger points very fast (rather like my ruger mk 2) and fits my hand very well.
I still have to shoot it to decide if its worth it.