Sorry for that. They dont make for a nice display piece but the casting inside is still MIP/B! I have one carded piece we won as a door prize you can barely see inside that another motorcycle collector later picked up for his collection as a loose bike.
It really depends on if you are an Abiogenic or Kerogenic viewpoint believer but the oil was there long before China existed. But I would still blame the algae overall, but then they are not a virus. Hot Wheels collecting can be hard sometimes.