With the threat of a 100 mile drive (this Saturday) as it's first outing, I decided I couldn't take a chance on the pump as it was.
The clack sounded like it was doing some damage, so about 12:30 last night I decided to pull the pump and swap the 10mm head for a 9mm one.
By 2:30am it was stripped on the bench.

My boss sent me home an hour early today so I cracked on with the pump and got it built, then the kids came home and I got sidelined with making dinner, running a bath, making the beds, reading stories and other manly things.
It was nearly nine when I was ready to bleed the pump, but it wont

1 and 3 spit a bit, 2 and 4 are dry.
With 1 and 3 unions tightened it nearly starts but not quite, if it would start the pump would clear in a few minutes - I hope it's grease used for the assembly that is blocking things up.