Nothing mechanical unless the steering head broke internally.
Yours is just stuck.
Usually the steering tube is dirty and needs cleaning and or heating??
Now that it's became a problem?? Don't make it worse by just trying to add grease.
The motors 26 and probably still has the original grease in there.
You need to add grease but only after heating the old grease until it melts.
If you try to add grease now you can push the grease fitting out, then reinstalling them can be fun.
Sometimes the steering cable can be locked and needs to be replaced.
Unhook the steering arm from the engine and see if the wheel turns.
If it turns? then the kingpin is frozen.
Not frozen? Then the steering cable is frozen.
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I use a small propane torch first on the steering tube.
Have someone turn the wheel as someone heats the tube as someone pushes the motor.
Putting too much pressure on the wheel can damage it. Just turn and hold without too much pressure.(hope you understand)
Then try turning the wheel in the opposite direction as you heat the tube and push the motor.
Once the motor turns then get some rags and put under the steering cable end.
Spray with WD or PB or any lube spray.
Turn the motor back and forth, spraying all the time.
Your trying to flush the steering and the tube
Bad cases, take the steering cable out.
But a tube rush and hook to a drill and ream the tube.
Clean the end of the cable.
I use WD or any motor oil on my steering.
Grease get's in and hardens and your eventually stuck again.
Kingpin, heat the whole kingpin area, the top and bottom have bushings so don't over heat them.
Get it as hot as possible even heat the fitting.
Try to add a tiny bit of grease.
If it resists? More heat and try again.
Sometimes the fitting seizes and the spring and ball inside it need to be hit with an awl to make it move.
Use a good quality MARINE grease even a Lithium Marine grease.