I did this repair many years ago after the mounting failed on the X-300 (original single bold stub mast) which allowed the antenna to sway. It gave a few more years of service after the repair and mounting modification and was only taken down to be replaced with a new X-510 which has the same mounting modification.
The X-510 has been up for many years with no issues despite being battered by the winds and salt coming off the North Sea.
The modification to the stub mast. The section was turned upside down so the elongated bolt hole is at the bottom and 4 slits cut with a hacksaw.
A stainless steel Mikalor clamp is used to secure the stub mast to the base of the antenna and provides a much better fixing that the original single bolt.
My X-300 had started to show intermittent high SWR which had started when the stub mast failed and the antenna was swaying about. When I removed the radome it was obvious that the lower coupling capacitors had become damaged and there was a fractured solder joint. I replaced the capacitors with new parts rated for 3KV.
The last thing I did before replacing the radome was to put a small blob of threadlock on the screws in the joiners and then wrap them with a few turns of self amalgamating tape. This should prevent them from shaking loose in the future.
The X-300 is a great antenna and is still performing well. It’s mounted around 20′ lower than the X-510 but is great for local coverage. I find the X-510 is great but does move around a lot in the wind which can lead to heavy fading so the X-300 is my local backup!