1999 Mercedes-Benz Sl — MOT failures & pass rate
Across 3,177 MOT tests, the 1999 Mercedes-Benz Sl recorded an 87.3% pass rate. Coupes & convertibles of a similar age fail 22.0% of the time, so this is 9.3pp better than the group it competes with. Failures cluster in lighting & signalling, suspension and brakes.
What the MOT record shows
No single area dominates — lighting & signalling (6.7%) and suspension (4.8%) are close, so failures are spread across several systems rather than one weak point.
At component level the recurring items are ball joint dust cover, headlamp aim and rigid brake pipes — ball joint dust cover alone was recorded 148 times.
A 150k+ example is materially riskier than a 0-30k one: 22.1% versus 6.8%.
Advisories point at the next bill rather than this one: brakes was flagged on 25.6% of tests without failing them.
The trend is worsening — 11.3% of tests failed in 2021 against 13.5% in 2025, the usual pattern as a fleet ages.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 6.7% | 214 |
| 2 | Suspension | 4.8% | 153 |
| 3 | Brakes | 3.7% | 117 |
| 4 | Visibility | 3.1% | 98 |
| 5 | Tyres | 2.3% | 72 |
| 6 | Emissions & environmental | 1.5% | 46 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Ball joint dust cover | 148 |
| 2 | Headlamp aim | 89 |
| 3 | Rigid brake pipes | 66 |
| 4 | Individual direction indicators | 59 |
| 5 | Side repeaters | 57 |
| 6 | Stop lamp | 55 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Brakes | 25.6% | 814 |
| 2 | Suspension | 24.7% | 784 |
| 3 | Tyres | 14.5% | 462 |
| 4 | Emissions & environmental | 10.6% | 338 |
| 5 | Lighting & signalling | 7.0% | 223 |
| 6 | Steering | 5.3% | 170 |
Failure rate by mileage
Higher-mileage cars tend to fail more — often the most useful guide to real condition.
| Mileage band | Tests | Fail rate |
|---|---|---|
| 0-30k | 148 | 6.8% |
| 30-60k | 698 | 8.9% |
| 60-90k | 1,093 | 12.6% |
| 90-120k | 799 | 14.9% |
| 120-150k | 334 | 15.3% |
| 150k+ | 104 | 22.1% |
Failure rate by age
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 719 | 11.3% |
| 2022 | 651 | 11.4% |
| 2023 | 618 | 13.9% |
| 2024 | 605 | 13.7% |
| 2025 | 584 | 13.5% |
What to check before buying a 1999 Sl
On a 1999 Sl, lighting & signalling is what the MOT record says goes wrong most — it appeared in 6.7% of tests. Check these areas before you commit.
- Lighting & signalling (6.7% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Suspension (4.8% of tests): Worn drop links, bushes, springs or shocks — listen for knocks over bumps and check for uneven tyre wear. Typical repair: £150–£450 per corner.
- Brakes (3.7% of tests): Pads/discs are routine wear; binding, imbalance or corroded pipes are more serious — test for pulling under braking. Typical repair: £100–£350 per axle.
Repair costs are rough UK ballpark ranges to set expectations, not quotes — actual prices vary widely by car, parts and garage.
Frequently asked questions
How many 1999 Mercedes-Benz Sls pass their MOT?
87.3% of the 3,177 1999 Mercedes-Benz Sl MOT tests in this dataset passed — a 12.7% fail rate.
What is the most common MOT failure on a 1999 Mercedes-Benz Sl?
Lighting & signalling, recorded in 6.7% of tests, followed by suspension (4.8%).
Does the 1999 Sl get worse with mileage?
Its MOT fail rate rises from 6.8% in the 0-30k band to 22.1% in the 150k+ band.
Methodology & source. Based on 3,177 MOT tests. Dataset: DVSA MOT testing data (2021,2022,2023,2024,2025). Data last updated 2026-07-27. Figures reflect MOT-testable defects only — read the methodology for how these are calculated and what they don't measure.