Welcome to the forum. You'll enjoy our free Luger FAQ document which has years of accumulated Luger knowledge available:
http://forum.lugerforum.com/showthread.php?t=13121
If your Luger is cycling properly, don't be too worried about older springs. If you have concerns, search on "tape test" for discussions of marks on the rear of the frame and the recoil spring. The FAQ lists the various recoil springs used over the history of Luger production.
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.