Based on our shop experience specializing in heavy-duty brakes since 1985:

• Pushrod Alignment: Precision alignment of the pushrod is critical for GMT400 hydro-boost units. Even a slight offset during installation can lead to internal cup over-extension—the leading cause of immediate leaks.
• Hydraulic Flush: These units share a reservoir with the power steering pump. We strongly recommend a total system flush with fresh fluid; contaminated oil is the primary cause of internal valve sticking and seal failure.
• Accumulator Check: If you experience a loss of assist after the engine is turned off, the nitrogen charge in the accumulator is likely depleted. Our units are bench-tested to ensure fail-safe performance and proper backup assist.