It has not been any problem since that fix. Still working fine and the car has been in constant use. The front seat belt mechanism sits at the bottom of the B Pillar, the pillar between the front and rear doors. Basically where the belt goes in behind your shoulder and then down behind the trim to the mechanism at the bottom by the floor. To get to the mechanism is not hard, if I remember right you undo the belt guide behind your shoulder, unclip open the plastic clam cover and a spline bit and the plastic comes away quite simply with bit of gentle levering with a plastic trim tool. I think I may of had to unclip or unscrew some door bottom trim pieces but I can't remember fully. All I can say is it was pretty obvious when doing it.
Once the mechanism is seen then it can be unbolted and the electrical plug can be removed, that is the crash pre-tensioner. You can see the spline bolt holding it in at the bottom of the 1st photo. With the mechanism in my hand like the 2nd photo above then there are a few little holes in the white casing. As said earlier I pulled the belt out fully and sprayed silicone lubricant with the straw on the can through those holes. I also put some on the exposed gears the other side. While spraying I moved the belt in and out. Also manoeuvring the whole unit around to get the lubricant around the inside gears. Repeating at a few angles and different holes until I was happy.
As said when all put back together it has been fine over a year. Make sure you have a set of spline bits, xzn bits, as you need them.