Replicator 2 Y axis slipping?

I've got a Replicator 2 with about 350 !580! printing hours. It suddenly started slipping in the Y direction.
- The belts are all tight and I can find no damaged teeth or unusual wear.
- And the XYZ step motor cable has been replaced already with a crutch to help it not be bent in the future.
- The gantry seems to be aligned.
- I have yet to grease.

I'm not sure how to continue.

img of print with slipping ----> [IMG]https://www.dropbox.com/s/ni6gz1vr93sl83r/20170221_145312.jpg?dl=0[IMG]
Video of slipping -----------> [VIDEO]https://www.dropbox.com/s/fdm9qsbcv4qk8s2/20170221_141055.mp4?dl=0[VIDEO]



UPDATE: I replaced the short Y belt with a spare salvaged from an old bot. Tighter than the original but not as much as I want. ALSO IT STILL SKIPPING AROUND. :mad:
also this bot is at 580hrs :\

Things I have done:
-Greased
-Tightened all belts
-Realigned gantry
-Switched Y motor with a spare
-Switched short Y belt with spare