I'll warn you now, three things you need to know:

1. Removing the old thermal paste will take forever. But don't skip out on it, or try to force it off. Be patient. It doesn't have to be completely removed, just something like 70-80%.

2. Get the right size screws. Seriously, they are hard to find, but go to a large hardware store, because if they are longer you will either screw the heat sink broken, or be unable to put the motherboard back in the container.

3. Just use the nylon washers, one on top and one under. Don't use metal ones as well, because it will be too thick and you won't be able to fit the motherboard anymore. And for the love of master chief don't use metal ones only, unless you want a static shocks crashing your motherboard.

For the rest, if you have problems, just ask. Total cost for repairing is something like 15 euros, a lot better than 150 for a new unit, so definitely something to try.