The Bosch data says the union is M12x1.5, and it looks like a swivel conical joint hose barb.

Of course I cannot find said hose union, mine is siezed and horrible, want new shiny one for new hose and pump!

I can get M12-6mm hose or BSP 1/4" to 8mm hose, BSP will probably fit but not strongly, will be loose with less than ideal engagement 11.9mm female.

Have I got something wrong?

Measuring the male threads on the pump its more like M14, doesn't seem to be correctly indicated on the Bosch data.