Having spent many frustrating hours taking my 14 apart, and checking everything, and then struggling to cram everything back in place to put it back together, I have a nice smooth running unit on DCC (using a TCS chip). The erratic running issue I had was solved by tweaking all the wheel pickups, so that they bent further outwards from the chassis and contacted the (cleaned) wheel backs much more reliably.
Amazingly (for me) I have managed to retain all the extra bits to add on (although I did manage to break both sets of steps off too!)
My only remaining issue is the supplied couplings. They are way too short. On other stock, the tension lock coupling bar is generally on the same line as the buffer faces, whereas if the Class 14 couplings are pushed home, they are too far back, and don't swivel through the slot in the buffer beam.
Has anyone sourced viable replacement couplings, or found a reliable solution please? I suppose I could just glue the existing couplings into the sockets and hope the glue is stronger than the weight of any trains it hauls?!?