There are two lengths of those bolts. The thickness of the metal brackets is your clue as to which bolts go in which holes. The wave washers go between bracket and seat, not bracket and bolt head. The thin, flat washers go under the bolt heads and are somewhere between cosmetic and functional. Be easy with them. The 17mm flat sides of the bolt heads touching the washers need a quality 17mm open wrench, some common sense and a little luck to end up with a win-win ending for all . Dave's new shop rules include: no bleeding and no cross-threading of any fittings. There's more rules, but these two might get you through this job.