I had to pull off my fuel injectors. I had two that were leaking.
Seems they were leaking not at the top but rather at the manifold.
Can I just put new o-rings on them or do they need to be replaced?

And while ther eout is there some way that O could clean them before putting them back?

 

New O-rings will probably work if that's the issue. If the nozzles are dirty you can clean them with a spray solvent like brake cleaner or something that leaves no residue and evaporates quickly.

However, the O-rings might not be the problem and you might be looking at replacement of the injectors that are leaking.

 

Replace the O rings period. Rule of thumb, if you remove the injectors you replace the O ring.

 

Exactly! Replace ALL the o-rings both top and bottom. Ounce of prevention is worth a pound of cure.