If your yurt cover is made of canvas, it’s very unlikely to have failed within three years unless there is obvious damage to the canvas. The most likely cause is that parts of the stitching may have failed. If the leak can be traced to the seams then it’s possible to just treat the seams with a good waterproofing product such as Fabsil without taking the yurt down. The best way of doing that in situ is to buy a small paint roller (the sort you might use to paint edges of walls), soak it in the Fabsil and run that up and down the seams until it’s thoroughly soaked in, you can always use an extension pole to reach higher up. Choose a nice day to make sure the Fabsil has plenty of time to dry thoroughly...and do wear a face mask to protect yourself from any fumes. Good luck and if that doesn’t solve your problem you’re welcome to contact me for further advice.