are you using OEM parts? or aftermarket (TVH) part?
my thought is either a lesser quality aftermarket part or an alignment issue. Could be something in the steering gear or steer unit binding up putting too much stress on it. Even something as simple as the incorrect type tire on the steer wheel(s) can cause excess strain on the system and cause something to break. Rubber tires are pretty hard on these types of steering units, does it have rubber or is it poly?
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