sand and paint them
If the rust has not eaten all the way through the metal, then in principle it is possible to sand off all the rust, and repaint. But running boards are not that thick, and you probably don't have enough metal left to do this successfully.
If it is "rusted out" you do not repair it, You do replace it with XHCI
Yes but with poor results. How about cutting the rusted metal out and replacing it?
No
Where's the leak? Wheel cylinder, repair or replace, rusted line, replace, master cylinder, repair or replace.
You have exhaust leak where the pipe rusted through and this makes the loud noise. You can go to a parts store and get a exhaust repair kit to fix the hole. This is only a temporary fix and might not be enough to fix the repair. Otherwise, you have to go to a muffler shop so they can replace the rusted section.
With a welder, fabrication and some Patience.
If they are beyond repair, I cut them off with a thin metal cutting disc in an angle grinder.
Depending on the amount of rust you can bondo the holes. You will ned to cut the rusted parts. If the area is large then fiberglass will make a better and more durable repair than bondo.
I am about to start the same project, it's worth a shot !
First remove the paint around the rusted area, grind down the rusted spot, then paint over the spot and cover the rest of your car you don't wish to paint with something like newspaper.
The cost of the fuel line will vary depending on the parts store. If you decide to have a dealership repair the vehicle, you will also have the cost of labor.