There's been some interesting traction on the sleeper sections under the wires this week by all accounts, including 86401 doing the up Highlander one night and a variety of locos on the Lowlander Edinburgh portion, including the Colas 47739 and - for the first time - a single Class 73 (73968).
Added to that, unmodified/grey GBRf 92 92044 got in on the act mid-week, giving 86401 a lift back to Glasgow on Tuesday night and has done a full run every night since.
Meanwhile 92023 has had a trip up to Crewe for a training or route learning/retention run yesterday to Preston and back via Earlestown and Newton-le-Willows, and then on to Nuneaton and back via Stoke, Stone and Stafford both ways.
Things started off fairly normally on Sunday night with 4x 92s (92010/014/018/023) working the main WCML runs and Freightliner 90043 on the Edinburgh portion. All then went a bit awry on Monday night...
From various bits of info I believe the following happened, but please feel free to add/correct any of this:
90043 worked the Polmadie Edinburgh portion ECS to Waverley - I'm assuming it was planned to work it back to Carstairs, then do the Edinburgh-bound portion in the morning as everything that followed was on VSTP paths.
90043 presumably then encountered some sort of issue, as didn't make it back to Carstairs and subsequently went to Craigentinny the following day where it's stayed since.
92010, which was stabled at Edinburgh on Monday ready to take the Highlander southbound in the early hours of Tuesday appears to have been subbed in to take the Edinburgh portion to Carstairs, then stayed on and hitched a ride with 92023 and the Glasgow portion to make sure it ended up in London as planned.
Meanwhile, 86401 having taken in the ECS (+92023) to Glasgow, then moved directly to Edinburgh on a VSTP path where it then hauled the Southbound Highlander from Waverley to Euston.
86401 was most likely booked to do the Glasgow-Polmadie ECS working the following (Tuesday) morning, but was now in London. So appears that once 92018 had brought the Northbound Highlander up, it went to Mossend temporarily, then into Glasgow to work the ECS back to Polmadie.
Meanwhile Colas 47739 worked the Carstairs-Edinburgh portion and ECS return to Polmadie on Tuesday morning.
There were further interesting traction options on Tue night/Wed morning as "misplaced" locos were returned. 92044 joined the fray (with 92023 going off for the training/route learning mentioned above). 92044 hauled the northbound Lowlander to Glasgow with 86401 tucked in behind. 47739 was then allocated to the Glasgow ECS moves (with 86401 on its overnight jaunt to London).
92018 relocated from Polmadie to Edinburgh to be in position to take the southbound highlander forward in the early hours of Wednesday - I think it may have taken the Edinburgh portion ECS with it to Waverley although not 100% sure. 73968 then made a rare - and debut (in terms of a 73 on the Edinburgh portion) - appearance to work the Carstairs-Edinburgh portion.
Since then things have largely settled down with 92010/014/018/044 working the main runs, the Colas Duff on the Lowlander Edinburgh portion and 86401 back on the ECS. Meanwhile 90043 remains at Craigentinny.
EDIT: see captainbigun's clarification/corrections in post below...