the bottom guide pin bolt won't go on.

Solved with a G clamp pushing the bolt in and two open ended spanners.

Found a peculiar pad and disc wear pattern. At the caliper piston side, the outer edge of disc is raised and rusty, and the front part of pad is recessed corresponding with this. I wonder if there's any faults with other components that could cause this?

that rust i dont think is only rust, it has to be something a little harder, maybe concrete sediments from a construction site you passed and got hard in the edge of your disk or calcium deposit from hard water you slushed wich is eating the brakepad, just sand it down and it be ok (i think) but it doent look like a biggy

here when the brake disk is uneven (like that) there is a machine that smooth the surface, they call it rectifying the brake pads when you do, braked always grip better

Chip the rust off the edge of the disc all the way round with a little toffee hammer. Chip radially inwards.

This happens on a lot of disc/pad combinations. The main pressure is on the middle of the pad, and a little rust buildup around the edge of the disc easily lifts the edge of the pad up around the edge. From that point onwards, it's a vicious circle.

:confused:

how much is a new set of discs anyway??

edit: btw that.s probably been caused by fitting a new pad to an old and knackered disc

Have fitted new discs and pads anyway. New discs £ less than a tank of petrol Was concerned it may point to a fault elsewhere which would affect new disc - but seems it's just the disc then. Test drive tomorrow hopefully.