I should add that I have used the bike shop for smaller jobs in the past, and they have been very helpful. They did a pedal swap (I don't have the right tool) for free and even replace a missing bolt, also for free.

According to the paperwork they gave me, they will replace the cassette if needed. They weren't giving me the hard sell, but I think it will end up with them suggesting it. I have a feeling that cyclezen might be correct regarding cassette wear.