Very tedious. If I had gotten it on the first try, it would have been worth my time. Taking it apart a second time and doing a better job took a second hour, and I should have either done it better the first time or gotten a new part.

If you do try to solder it, here are some tips that I learned. First, use a small die grinder (or Dremel tool) and grind the tips of all of the high-current leads until you see the base metal: the bars and the high-current relay contacts. Solder them with a powerful iron. This will help the solder bond to the connector.

Use a big enough heat source to do the soldering. I used a butane-powered iron the second time, supposedly 180W equivalent, but it worked much better than a 140W electric soldering gun. Don't even bother trying to solder these with a standard soldering iron. It won't get the joint hot enough to get a good bond.

After soldering these, let the board fully cool and solder the coil connections for the relays. You will almost surely have moved the relay position on the board just enough to make these fail; I did. You can use a standard soldering iron for these, and I recommend it. You don't want to damage the relay coil connection.

If mine fails again within the next ten years, you can probably guess what I'll do.