SGS sell top quality gas struts.
https://www.sgs-engineering.com/car-boot-tailgate
They aren't welded into place- they couldn't be- there is a clip at each end with a recess behind it. Wedge the boot open with a piece of wood, place the tip of a flat-bladed screwdriver behind the clip and into the recess and twist it, the clip will pop off. When you have done both ends the strut will just pull off.
The new strut can just be pushed into place. It takes maybe two minutes to change both.