As I mentioned before the 1308 Milford Haven to Manchester which starts in Manchester at 0630, is often a 150 instead of a 158. I guess it must be difficult with the 158s as the cambrian obviously takes priority so if there is less availability of 158s then the South Wales diagrams suffer. The afternoon/earlyevening Gloucester-Cardiff-Fishguard is often a 150 for this reason,
I also dont think a 158 should be used on local journeys like Ebbw Vale and Maesteg, not with them now being refurbished and including nice comfortable seats and power sockets. any "spare" 158s should be on long distance like Manchester to Cardiff to take pressure off the 175s but i appreciate it isnt possible to diagram them. Im amazed they still come to Cardiff to be honest, their maintenance is done in Mid Wales is it not?