Hi
Those pipes may well be the ACE pipes that run on top of the chassis. Mine are really rusty as well.
I have a similiar yellow liquid as you down below the radiator. It's sort of behind the rad. I am losing a bit of coolant over time but not any PAS fluid, so I was assuming that the yellow colour was the orange coolant mixing with all the oil lying around down there.
I've a new radiator ready to fit and will waxoyl the ACE pipes when I have the rad out.
If you find out anything else let me know.
Cheers
Andy