Lectric window

Well i've fitted the new seal to my drivers door window and while it was off, tested my theory that it was the knackered seal that was causing the window to slow down when lifting and lowering... to my dismay (but expected dismay!) it wasn't

Anyway, the new seal was fitted and I started checking the mechanism, all the rollers are intact and plenty of grease on the runners...

The gearwheel was dry, so i applied a smear of coppaslip

Watching the mechanism it 'sticks' when the main arm is roughly horizontal, removing the mechanism from the door it all seems free...

Any more ideas to what could cause this slowing?