Leaking injector bore on '96?

My 96 2.2 L S10 has been leaking around number 3 injector for weeks I've replaced the O-rings to no avail I've even taken in an injector from a non leaking position and put it in that bore and it has leaked. There seems to be a ridge about a quarter inch down from the top of the boar but it's not where the O-ring seals. Can anyone tell me if I can resurface the bore with sandpaper or steel wool without making it oversized. On a related note, is it necessary to replace the O-rings every time you pull the injector? Finally, if the tines on the injector retaining bracket are bent or misaligned, can that cause the injector to leak? Any information that anyone can give me would be greatly appreciated.

That step in the bore is normal (see below):

http://www.wwdsltd.com/files/134InjectorRemoved.jpg

It would be acceptable to polish the bore with a Scotchbrite pad, but don't use sandpaper or anything that will potentially leave embedded grit in the soft aluminum - It will never seal that way. If it has been sanded, you may be able to hone the bore and then clean it thoroughly, which might possibly require removal of the head.

Straighten the bracket as best you can to insure the injector is fully seated and square/flush. Apply clean engine oil to the O rings before inserting the injectors into the bores. New O rings are not necessary if the existing O rings are not scuffed or distorted.

Thank you very much for your informative response. Especially your info about the o-rings. I've been going thru o-rings like nobody's business.