Chains dont need changed the 320d with the n47 have problems with the chain snapping but dont think the 525/325d have this issue, I have a 320d m sport the suspension is ok once you change tyres to non run flats,
I haven't removed my swirl flats yet its a 320d 57 plate with the m47 engine im not sure these are affected with swirl flap failure
mine has done 70k but have seen load with 150k plus still going strong just make sure it has fsh and nothing is missed out great mile munching engines in the bmw diesel range