The 149 has been around a long time, and guessing you are not the first owner, so you have no idea if the usage.
Anything from gentle usage just mowing a smooth lawn to front loader abuse.
the spindles are inserted in the stamped then formed bracket, and welded to it on the inside stub.
we have no knowledge of the quality of the weld, the conditions of it at time of manufacture or how the molecular structure was disturbed by the welding.
Most all spindles work just fine, obviously this one failed.
it could have caught a tree, the corner of a building, some youngster doing "wheelies" etc etc.
We could speculate for many lifetimes the "why" it failed.
They did see the need to go to a larger 1" spindle in later models.
possibly they also used different material for the shaft itself or changed the welding process.
Did it break off leaving a short "stub" in the formed bracket, or did it fail at the point where it was welded on the back side at the end of the stub?
Actually, it doesn't matter, it is "done broked" as is said
There is no "adjustment" as such for the bearing, like on a vehicle with a spindle nut & cotter key holding the hub/brake drum or disc to the shaft.
Just replace it and don't buy a lotto ticket for a while.
You are actually lucky, as it could have decided to divorce itself in an event that was dangerous, or quite embarrassing with 50,000 spectators watching.
