Ok so I had 10mins to spare when I got in from work so went to try and get a better look at this gear linkage. To hopefully work out why it's jumping off the guide pin at the rear.
Here is what I found.
Bushes missing from the guide pin itself and the bush insert missing from the end of the rod itself.
Ball bushes on the relay lever worn and slid to far up. But none of this I can see would cause the rod to jump the guide pin.
Next checked the clinch bolt, my thinking here was that if the clinch bolt was loose the front and rear rods could slide completely together. This would make the overal length of both rods as short as it could possibly be. So maybe when moving the gear stick into 4th this would be enough to pull the rod off the rear guide pin.
The clinch bolt seemed tight, but the front rod did look as if it was pushed all the way into the rear rod. I could see no splines protruding.
Next i tried to take a look at the front linkage below the gear lever. Unfortunately I didn't have time to drop the spare wheel to get a proper look. But I did get a photo. The linkage looks to be in place ok and you can see wear on the inside of the box, but with the rod not attached to the replay lever at the rear I'd kind of expect that with the extra travel it has.
I'm going to replace bushes etc where ever they are worn or missing. But I'd ideally like to work out what caused this.
What's people's thoughts?