Any question answered...

Checked that the middle chainring isn't worn out?

As the 52 ring is knackered you might as well change it. Setting up the derailleur isn't too difficult. I'm sure there are guides out there. General guide though - 2-3mm above the outer ring when centred above the ring.

http://www.madegood.org/bikes/how-to/set-up-a-front-derailleur/