malfunctioning luger

[robin1]

i have just purchased my first luger. it is a 1917 9mm erfurt in very good condition. unfortunatly it malfunctioned the first time i fired it. almost every time i fired it the spent casing remained in the chamber. a few times the spent casing got caught between the bolt and chamber partially extracted. the extractor appears to be ok. could it be a weak extractor spring? if so where can i find parts. i have checked with numrich and northridge. no extractor spring with either of them. i am not having much luck finding any luger parts.