I did mine a few days ago. 16v JTD.
I bought 4x washers on ebay (gen Bosch, cost £7ish). No need to anneal a new washer, or buy a tool to remove them. Luckily for me, I spotted the leak early and did very few miles in that condition so the injector came out easily, with minimum mess.
In short, remove injector pipes, unbolt injector clamps and prise the injector out. This stage can either be simple, or a flippin nightmare!
As has been said, the longest job (if injector comes out ok) is to clean all the horrid goo/ carbon/ gasses that have worked their way past the seal, up the injector tube and collected at the top of the cam cover.
The ebay seat cleaning tool looks good, but I just cleaned mine up well with carb cleaner, various implements and some decent rag. It takes time, but well worth doing properly.
My engine is so much smoother now there is equal compression on all pots