Frustrating window problem

My windows have gradually become harder and harder to budge over the last few months and now they're finally knackered. It's a 1983 tintop with wind ups. 

They seem to be okay going down but when it comes to getting them to go back up, they will not move. I've had to take te winder handles off to reveal the small metal cog behind, and struggle to turn it with pliers. 

What is it that needs replacing exactly? Is it the winder mechanism itself? Anyone know where I can pick them up if so? 

Best bet 1st would be to remove the door card and have a look at what's going on. Get some lubricating spray and make sure all moving parts are done and also the window channels. Hopefully might just do the trick.

Dan

Make sure nothing is blocking or lose in the channels which the window runs up and down, might also be your window needs adjusting have you tried grabbing the window and seeing if it windes up any easier if you pull the window/glass forward or backwards or pulling it up?