(9 hours ago)PH - BQA wrote 7564 has an intermittent issue with its retarder at high speed I believe.
7547/8 have been dodgy for a while, so they may just be kept local for the time being. 7548 in particular has been a dog for a long time, including pre and post new engine.
Thanks for that, had a feeling there was something wrong with them. Noticed 7548 is the one pretty much living on the 57/57A which has seemed to become the new 35 where anything broken ends up on I've noticed.