(17 Nov 2017, 7:25 pm)V514DFT wrote Why was 4512 kept instead of anything else from that batch (4501-4515) bar the ones that became driver training vehicles,was stuck behind it today and the decibels coming from it were ridiculous

Arriva likely didn't choose that to stay longer over any of the rest of them, just a unique sequence of events that led to that being the case. Others, I believe, had ceased engines, some may have had other issues that became uneconomical to repair, 4503 was obviously written off. Same question could be asked about 7439.

Would have depended on whether it was needed when it was due to be withdrawn, if they needed to keep it on they would have.