Are you sure you are comparing the right lines?
The B sparepart line is 120cm and the C-spare part line is 100cm..
Double check them again.
If they have shrunk that much I would recommend changing them.
Also to dramatically increase sparepart line life regularly spray them with SailKote by McLube.
Same thing with the pullies.
SailKote is a dry lubricant specifically formulated for Sail Cloth, lines and rigging hardware.
Sounds like you have put many hours on the kite so it would be a good idea to change the pullies too.
Here is a litle video to show you how get the new pullies on. Can be tricky to figure out, but it's real simple if you know the trick:
[kiteforumtv]http://www.kiteforum.tv/video/flysurfer ... _knot.html