The terms and conditions of your warranty should detail what is and is not included, but we would suggest contacting your dealer regarding this issue. Ideally they will replace the pin or bush under warranty, but even if this is not covered it is a relatively inexpensive repair. While it is disappointing to have an MoT advisory at such low mileage, a car that has covered so few miles in three years will have been left standing for extended periods of time, which can cause rubber components such as bushes to degrade.