Any Ford diesel specialists on here?

[Oscar]

My 07 Focus requires a new injector seal. It was leaking slightly for a while, but yesterday went completely and left me at the mercy of the AA man and his recovery truck

Although looking at it, I can see nothing which looks difficult to do, has any one any experience of replacing these before.? Would I be wise leaving well alone and having it done professionally?

PS: it's a 1.6 tdci