injector removal and reseal?

I have the dreaded fumes inside the car, astra 1.7dti ls eco 'Y' reg, I am led to believe that the injector seals are normally the culprit.If so how easy to deal with, and while I am here,the plates which hold in the injectors in place, do they have a oil seal gasket? Help!! I am not completely mechanically thick but any help would be appreciated, as to any pitfalls which may come my way, thanks in advance.