I am not that clear what can go wrong with a 2008 520D manual (108k miles), in my head it is:

1. Turbo
2. DMF
3. DPF
4. issue from Swirl flaps? wrong engine/generation?

so if a Turbo has been replaced with BMW recently, there would be a 2 year parts and labour warranty on that. What are the costs of the others? How bad can things get if I very rarely go on 100 mile journeys, is that is what is required to clear filter?