If you regularly use one gear it's quite possible it's more worn than the others, unfortunately you can't just replace a single sprocket though.
that's true but there's no wear that I can see.. plus the cassette has less than 1k miles on it

If you regularly use one gear it's quite possible it's more worn than the others, unfortunately you can't just replace a single sprocket though.

Could just be derailleur out of alignment?
It can catch on the bigger gear then jump back down to the smaller gear and it feels like the chain slipped round.
Get the bike up on a stand and try pedalling it with your hand. If it still does it, it's catching on the bigger gear not slipping.
it was working fine yesterday in rain! but I'll have to check it anyways as it's quite loud so you could well be right 
Fails for not adhering to OCP rules![]()
Fails for not adhering to OCP rules![]()

Very close though!
He's even matched up tyre logos with valve stems.

It's the wrong way round!

