Recently I looked up some parts costs for the owner of a B8200 with manual steering.
When I told him the cost of the complete box (according to Messicks) which was around $800 he said all he wanted to do was rebuild it and all he needed was the ball nut and a few bearings and seals. The cost of the ball nut was more than the cost of the complete box.
The trouble with trying to repair stuff on these L tractors is that there are no high quality workshop manuals nor are the parts illustrations very good quality.
Buying a complete assembly helps those who do not do these boxes on a regular basis.
Your loss of steering is likely the rusting out of the small tubes on the outside of the ball nut.
The photo is not of a L225 but typical.
This short video will show you the concept of recirculating ball steering.
https://www.youtube.com/watch?v=OeokGSdVTAg
https://www.youtube.com/watch?v=qD00DIGVhtk
Dave