Recently had an issue with my vacuum valve not working so have replaced it. Sadly, it's still not holding a green light so seems the problem was greater than that single issue.

I can't see anything obvious so was hoping for some guidance on trouble shooting it to see if i can find the issue and fix it myself. Any ideas?

Unfortunately you most likely have a leak somewhere. Could be any of the buttons ect with an o-ring.

You could try to use leak detection smoke to pinpoint where it is, but if its really small, it might be useless.

Your local dealer can service and change everything im sure.