Our umbrella will not stay straight up. I will automatically tilt to one side. The other side we have to still push in the button. There is no obvious damage/breakage. How can we get it to stay straight? We typically don't tilt it ever...

Maybe the shaft (pole) would fit inside a section of schedule 40 PVC pipe, if you can match it up to a pipe of a diameter that provides a tight fit. Sounds like the knuckle that allows it to tilt is broken. A piece of pipe just over the knuckle might work too.

If you have your manual for the umbrella you can call customer service and order a new tilt mechanism for it