Hi,
I had the same problem. There's a post on here somewhere (I looked but I couldn't find it) that described the right way to do this.
It was something like this.
Of course you need the washers in the right place but build up the arm but don't put the bolt through the arm yet. Hold the rear washer in place with the rubber seal but for the but on the front end use a little bit of lube and get it up on to the outside of the arm. Put the arm and the washer in, slide the bolt through the first hole to hold it basically in place and on through the full arm, then slide the rubber down over the washer to hold that in place, then slide the bolt right the rest of the way through the arm.
The point was that with if you put the washers and rubber seals in and then try to slide the arm in, it usually binds. Doing it this way the rubber isn't in the way and easily slides down over the washer when required.
When I did it this way I didn't need to rub off any of the paint.
Worth a try before rubbing off your powder coating.
Rod