Is this solution legal?

Is that rtv?
I welded an oversize washer to stop a leak in the same place, until I could replace the steering sector.
Don't know if it was legal, but it worked.

 

I do not remember reading where there are regulations on what type of seal has to retain the oil. However that is a halfway repair and could be a precursor to a internal problem. Instead of worry about if it is legal I would worry about if it is safe. It maybe a little different if you are just running around town but if you are running the road a break down will cost you many times over doing it at home.
Running it low on oil repeatedly can cost you a pump.
Thank that is just a dust cap and the seal is inside. Not a job for most people.
Don't take chances on steering and brakes!

 

I second the notion of the safety aspect being the primary concern.