Injector leaking at block (300tdi)

Afternoon!

Opened the bonnet the other day (always a bad mistake....) and I noticed that fuel was leaking from the injector as it goes into the block. I've looked at tightening it up, but it hasn't really shifted, and I didn't want to tighten any further incase I wreck it completely. So my question is, do they tighten up really well, and can they take a bit of stress (am I just being a jessy) - if they appear really tight, and still leak, do I replace it?

Cheers
K

is it your pipe to injector that is leaking or the injector as it goes into the cylinder head?
If its the injector to head seal it may require a new copper washer at the base of it. Or is it even the return feed pipes that are perrished and leaking?