Hi Peter,
Sorry to hear how frustrated you feel over the above problem with your crossings & the Class 08. I had the same problems with my 156 Sprinter departing the station, then after a load of testing without a fault, my large logo Class 47 was derailing Mark 2 coaches on the bends at random. It does get frustrating, especially when you work hard & want to sit back & enjoy the layout.
As the others have said though, sometimes it's best to walk away from it for a while then go back to it after a couple of days or so, & then adjust what you need to.
I'm in the process of remodelling quiet a bit of track in my station & altering the bends....in hope it'll work.
If your deciding to start again, then i'll look forward to what you come up with as your modelling is brilliant, & Llanbourne is one of my favourite threads on the forum. I'd be really sorry to see it go....
All the best,
Mark