Bonnet / Boot Gas Strut

What is a Bonnet / Boot Gas Strut?
Bonnet and Boot gas struts are essentially shock absorbers for the bonnet or boot of your car. They are angled in such a way as to provide an assisting force when opening the bonnet or boot but this force is easily overcome by the force of closing. So they provide both a soft closing action but also take much of the weight of the boot or bonnet.

Over time these parts can wear out and should be replaced, they are generally quite an easy DIY fix.
What problems can be caused by this part?

Bonnet does not open or shut correctly and / or does not stay open

When opening the bonnet it gets stuck or won't hold its weight when attempting to open. When fully open the bonnet won't hold it's full weight and drops to close.

Boot is noisy when opening and closing

When opening or closing the boot it makes a loud creaking or mechanical noise.

How much does it cost to replace the Bonnet / Boot Gas Strut?
Expect to pay anywhere from £10 to £50 for a pair of replacement struts.