Common problem for rears to corrode, after all it's an 8 year old car in the UK. £250 to replace ALL the pipes front to rear is very cheap. There's a lot of work to do it. As above I've done it.
I agree with other that it does depend on the tester, although you agree they are poor, so a good 'catch'. There are many posters here who get an advisory one year and nothing the next...
You have no cause to go back to people servicing the car. They are changing oil, filters, etc. not doing a pseudo mot, although some may see it and make comment.
Fuel cap is being picked up more often. Was an advisory on mine last year so replaced with a new one from Ebay for £20
Indicators is an odd one. They use orange coloured glass domes over white bulbs to create the colour, so don't peal or fade. I don't see how they can not be orange enough, however you could just change all the bulbs to amber too.
