They do no need lubricating, Bricky, but much of the mechanism is inaccessible in most doors and windows .
I'm not sure that's strictly the case. I have removed various mechanisms locks hinges etc and there are many websites, Screwfix included, but not exclusively, that supply either the direct parts or suitable common parts based on various dimensions of the plastic profiles. I have just replaced some window locks on daughters new house. Previously on my house and my Mothers house and I am no expert, trust me. Still managed to solve the issues.
Oh yes and when moved in to the current house stripped all locks out and mechs gave a good lube up and no issues since 10 years on, they were well gummed and stiff when we moved in.
Alan