It depends on which one, upper or lower, and perhaps which side. OEM ones are plastic, you can get cast aluminium alternatives from the USA which probably last better.
I'm in the process of swapping mine. All 4 for the Ali ones from the states. The uppers are apparently a pain to do. And my engine ended up coming out. The costs then went skywards as I started replacing all sorts of stuff that was accessible while the engine is out.