My advice, play around with it.
You said it yourself you're going to be getting something better next year so why not take it apart, try to fix it and learn a few things right now?
It could be compression and the spring as well. I have heard the springs they use don't like to keep their stock strength or something and will usually "settle" after a bit of a break in period. Couple that with possibly leaving the spring compressed and an air compression problem and it could add up to something more like 20-30 FPS drop. Sure it may seem like a 100 FPS drop but that's only from observatory judgment on your part. I don't doubt that it probably did drop but not by 100 FPS.
So, get over to the doctors corner and take some of the things said here into consideration and once you feel confident enough open it up and try to keep a log of where everything goes (also good idea to take pictures in a well lit area just in case something springs out or you have extra pieces when you put your gun back together.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE