I found that one of the white plastic spring-loaded pins (see picture) which hold the heatsink down had not been seated (pushed through the board). It took a little force but once I pushed it through the heatsink no longer wobbled/tipped away from the board of it's own weight. I could pull it away but it didn't fall away. If the pin moves up and down while the heatsink is pressed against the board the pin is seated -- if not, it probably isn't.
I kept the board. I checked the processor temperature regularly for the first few hours of operation, then less and less frequently. I still check it occasionally. It runs a little warm and I'd worry about this if I overclocked but I don't.