So the 915 gave up on me, not surprised as it took a lot of stick (pardon the pun). During spirited driving 2nd gear decided it didn't want to go in at all. I managed to limp it back to the unit and we drained the box to find a lot of dog teeth loose, I was surprised as there was no grinding prior to failure.
The first and second gear dog rings had no teeth left and the synchro had fell out! Luckily this was the only damage and it was a relatively cheap fix (for a 915 box).
Now the box and engine is back in, she shifts into first a lot easier and the judder when pulling away in first has gone! Engine speed increases quicker now with the aluminium clutch housing so I'll need to adjust my heel & toe. I just want to get out and drive it before the weather gets rubbish!