Oil is escaping past the seal in the damper. A light film or misting is often only recorded as an advisory; wording about a serious leak means there's enough oil escaping that the damper can no longer be relied on to control the spring.
Wording as it commonly appears on an MOT certificate: “Shock absorber has a serious fluid leak”.
What does it mean?
Oil is escaping past the seal in the damper. A light film or misting is often only recorded as an advisory; wording about a serious leak means there's enough oil escaping that the damper can no longer be relied on to control the spring.
How serious is it?
Usually recorded as: Major. The tester assesses the actual vehicle on the day, so your certificate is what counts.
What normally causes it?
- Age — the seal hardens and the rod picks up pitting that then cuts the seal
- Corrosion or stone chipping on the damper rod
- A failed top mount letting the strut work at a slight angle
What a mechanic would check
Look at how far the oil has run down the body and whether it's wet or just dusty-damp. Then a bounce test on that corner and a comparison with the other side, plus a look at the tyre for the scalloped wear pattern that goes with a damper that's stopped damping.
What might need replacing
- Dampers replaced in pairs across the axle — never one on its own, or the car's handling goes lopsided
- Top mounts and bump stops while it's apart, since they're usually tired by the same age
- Alignment afterwards on a front strut
Can you still drive it?
Failure item. Beyond the certificate, worn dampers noticeably lengthen stopping distances and make the car unsettled over bumps mid-corner — it's one of those faults you only appreciate once it's fixed.
Repair cost
Depends heavily on whether it's a simple rear damper or a complete front strut assembly, and whether it's a car with adaptive suspension — those cost significantly more. Ask which type your car has before assuming.
Before the retest
Suspension parts such as springs, shock absorbers and drop links are normally replaced in pairs across an axle so the car sits level and handles evenly. Any work that disturbs the steering or suspension geometry is worth following with a wheel alignment check, otherwise you can pass the retest and still wear out a new pair of tyres within months. Listen for the original knock again on a bumpy road before the retest — if it is still there, something was missed.
Retest rules
If the vehicle stays at the test centre for repair and is retested within 10 working days, a partial retest is often free; some items qualify for a free retest if you bring the car back by the end of the next working day. The exact conditions are set out on GOV.UK, so confirm with the test centre before you leave. A major or dangerous failure means the car cannot legally be driven away unless the previous MOT is still valid and nothing dangerous was recorded — check your certificate first.
Related help
More suspension failures · MOT failure decoder · Ask a mechanic about your certificate
This is general guidance from a UK mechanic, not a substitute for a physical inspection. Only the tester who inspected your vehicle can confirm what was recorded and why.