The rubber grommets that it sits on generally keep in a good condition, but there's usually a crust of rust/grime rust under the grommet, that has built up over time.
you can clean it off by scraping it with a small screwdriver, and wiping the crap off with a cloth, but make sure to cover the small holes (below the grommets) with something before you start, as you don't want any crap stuck in them.
One I did this weekend.

And Servo.

You should bleed the system as a precaution anway. Buy a litre of Dot4, as half will fill the res bottle and a bit more will clean the old fluid out.
But you could get away with not bleeding the system if you don't clean the crap under the grommets and just put the res bottle back on once you've finnished messing with the brake pipe.
If you're putting a new solid brake line one, then you will have to bleed the system, as there would now be air in the system.