Not sure why yours is failing but they are a pretty simple system.
When i bought mine years ago the window had been wired up with fencing wire to keep it up!! I had initially assumed the spline in the plastic handle had stripped and was surprised to find the butcher fix once i pulled the door trim off. Was a sweaty drive home with no opening window.
I bought a replacement mechanism and it was relatively easy to fit, just need to be careful that the glass doesnt drop or it may break, but it's not hard to do and the new regulator was relatively cheap.
If its working again then all good, if not I'd be replacing the regulator and be done with it. Good luck.
Dave