I have spoken with BA - it appears the OW tool is showing seats for LAN flights that are not actually available.

The flight in question was USH-BUE, which apparently has no seats from January through to the end of Feb?!

I've changed the flight to FTE-BUE but to my dismay the tool is giving me the same error.

BA rep is going to call me back tomorrow, but the travel prospects aren't looking overly positive for my very eagerly anticipated Patagonian trip