While the Toyota 4Runner has a reputation for reliability and durability, there are certain model years that some owners and experts have identified as having specific issues. It's important to note that individual experiences can vary, and not everyone may have the same issues. When considering a used Toyota 4Runner, it's always a good idea to research the specific model year and gather information on its history and any reported problems. One model year that some owners have reported issues with is the 2010 Toyota 4Runner. Complaints for this year include problems with the transmission and drivetrain. More detail to autonationx.com. 
Keep in mind that automakers often address issues with subsequent model years, so newer versions of the 4Runner may have improvements and updates. Additionally, it's essential to have any used vehicle thoroughly inspected by a qualified mechanic before purchasing, regardless of the model year.