If your extractor is still in there, you can worry them out some using the little diamond embedded dentist drills in a dremel or such. If you can't find the left hand drills (HF has a set) just use regular ones and get it to where you can either crush what is left with side impacts/prying with a punch, or pick out the spiral of thread metal.
Was the one you pulled out 1/4-28, or 1/8 NPT?
Worst comes to worst, drill the whole thing out, tap it something like 3/8 coarse and then drill and tap a cut off bolt/allthread for the zerk size?
Was the one you pulled out 1/4-28, or 1/8 NPT?
Worst comes to worst, drill the whole thing out, tap it something like 3/8 coarse and then drill and tap a cut off bolt/allthread for the zerk size?