Yesterday my gears were grinding, but otherwise working perfectly on my spare bike, so this morning I oiled them, and now it's slipping in every gear. Not skipping from cog to cog but actually jumping off and re-engaging onto the same sprocket on the cassette. I'm used to this happening when the chain and a particular sprocket on the cassette are terminally worn, but not instantly on every sprocket.
Also on the commute this morning the problem went away for a while, only to come back when I downshifted, even though I was putting less pressure on the pedals.
Any ideas? Sticky link on the chain or is it just worn out?