Hi Stu
I think you could well be right had this with the 4.6 loss of power, stop restart all OK then randomly lose power
New throttls body sorted it.
Good Luck
Dave
Morning Sammie
Welcome to the Forum
Timing Chain (BMW recommend betweeb 80 and 120k) is an engine out job so clutch and rear main seal at the same time I would guess between £1000 and £1500 depending on who does the work
Hope this helps
Dave