the expansion/contraction of hot vs. cold hydraulic fluid should not be enough to set off any alarm bells unless it's already low.

Take it to the dealer. I don't believe the hydraulic fluid in the steering or suspension are consumables. They should remain relatively stable. Take it to the dealer when you have time.

It's most likely a faulty sensor, or seal, but steering components are kind of important pieces of an automobile.... :-)

Probably a minor fix. They'll just send away to Germany and 29 weeks later they'll have the part in-stock and ready to install (pun intended) :-).