I think it looks fairly original and has clearly been off the road for some time as the ad suggests. The fact there is no air cleaner implies the engine was never displayed and I would guess the overflow pipe was disturbed long after it was last running but, out-of sight means out of mind and nobody bothered (or knew) to reset it correctly.
In my experience the average museum is not the best place for a car to be kept well maintained because their key priority is normally that it looks good but is will not be taken out and used. I have personal experience of a similar car displayed which was loaned to a well known UK museum in good running condition but, when the time came for the owner to have it back, despite looking nice it was virtually undriveable and had to be completely overhauled mechanically.
I would expect this to be the same but, as long as the coque is sound – and the price is right – it could be a good buy. Definitely not to be bought “blind” though.