Hello Stevie, they often look like that when they have been stored in Shetland sheds for years and your climate will be similar.
It was most likely tucked away in a damp environment for a while. If it was salt-laden as well, that's what we'll be getting. The efflorescence built-up on the parts is common for untreated aluminium. Even the speculum coating was naturally corroded away? Or the was it deliberately polished-off by a previous owner?