1984 Mercedes-Benz Sl — MOT failures & pass rate
The 1984 Mercedes-Benz Sl passed 83.0% of its 798 recorded MOT tests. That is 1.7 percentage points worse than coupes & convertibles of a similar age, which fail at 15.3%. Failures cluster in lighting & signalling, brakes and body, structure & corrosion.
What the MOT record shows
Lighting & signalling dominates the failure mix at 10.0% of all tests — 3.9 points clear of brakes, so it is the first thing to check.
At component level the recurring items are headlamp aim, service brake performance and component mounting prescribed areas — headlamp aim alone was recorded 50 times.
A 150k+ example is materially riskier than a 0-30k one: 20.0% versus 11.4%.
Advisories point at the next bill rather than this one: suspension was flagged on 20.7% of tests without failing them.
The trend is worsening — 14.6% of tests failed in 2021 against 18.2% in 2025, the usual pattern as a fleet ages.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 10.0% | 80 |
| 2 | Brakes | 6.1% | 49 |
| 3 | Body, structure & corrosion | 5.0% | 40 |
| 4 | Suspension | 4.6% | 37 |
| 5 | Visibility | 3.8% | 30 |
| 6 | Emissions & environmental | 2.6% | 21 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Headlamp aim | 50 |
| 2 | Service brake performance | 32 |
| 3 | Component mounting prescribed areas | 28 |
| 4 | Headlamp | 26 |
| 5 | Washers | 26 |
| 6 | Exhaust system | 20 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Suspension | 20.7% | 165 |
| 2 | Emissions & environmental | 19.4% | 155 |
| 3 | Brakes | 18.6% | 148 |
| 4 | Body, structure & corrosion | 12.3% | 98 |
| 5 | Steering | 9.7% | 77 |
| 6 | Tyres | 7.8% | 62 |
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 | 35 | 11.4% |
| 30-60k | 122 | 13.9% |
| 60-90k | 210 | 15.2% |
| 90-120k | 224 | 17.9% |
| 120-150k | 122 | 21.3% |
| 150k+ | 85 | 20.0% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 185 | 14.6% |
| 2022 | 182 | 13.7% |
| 2023 | 189 | 20.1% |
| 2024 | 154 | 19.5% |
| 2025 | 88 | 18.2% |
What to check before buying a 1984 Sl
On a 1984 Sl, lighting & signalling is what the MOT record says goes wrong most — it appeared in 10.0% of tests. Check these areas before you commit.
- Lighting & signalling (10.0% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Brakes (6.1% 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.
- Body, structure & corrosion (5.0% of tests): The one to take seriously on older cars — corrosion to structural areas can be costly and is an MOT failure. Typical repair: £200–£1,500+.
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 1984 Mercedes-Benz Sls pass their MOT?
83.0% of the 798 1984 Mercedes-Benz Sl MOT tests in this dataset passed — a 17.0% fail rate.
What is the most common MOT failure on a 1984 Mercedes-Benz Sl?
Lighting & signalling, recorded in 10.0% of tests, followed by brakes (6.1%).
Does the 1984 Sl get worse with mileage?
Its MOT fail rate rises from 11.4% in the 0-30k band to 20.0% in the 150k+ band.
Methodology & source. Based on 798 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.