Rear fuel tank overflow-breather

[John Cornforth]

Re. the filler cap. At one MOT the test was being conducted by a young lad under the watchful eye of the usual senior chap. He removed the filler cap and checked whether it had a sealing washer, which I thought was particularly thorough. Fortunately I had previously fashioned a ring from cork sheet to fit in it. I wonder if they had them originally, and whether that would prevent breathing via the cap ? Maybe the hole where the retaining wire fits would be enough.