A sliding door does not automatically need to be replaced when it becomes difficult to open or close. When the frame and glass remain serviceable, repairing worn rollers, correcting alignment, addressing hardware problems, or replacing an appropriate component may be a reasonable option.
Replacement may need to be considered when the frame is severely damaged, the glass is unsafe, compatible parts are unavailable, or the door has defects that cannot be corrected reliably through component repair.
The decision depends on the door's condition, available parts, safety requirements, and the overall repair needed. An inspection is the appropriate way to evaluate the available options.