not being funny, but with the time and effort involed in "fixing" the problem, you may aswell buy ALL the repalcement components (lifter, runners, guides, inserts around inside the doorframe) as these ARE 100% going to be a contributing factor to the faliure of your windows again.
The aforementioned fix is good, and will help, but it is inevitably going to fail again, and always at the wrong time (raining, on the way to a important meeting, just before you need to go in to work...)
Get the components needed, and then if you have the time DIY. if not then get it to a specialist , and i mean someone who HAS done this before, not necessarily a workshop at all
Your windows will function QUICKER and give you another 10 years WITHOUT problem if done correctly.
Please dont take this as a slight on Jessīpost as its not. More as a recourse for those it hasnīt worked for