Those stanchions are fucked. I wouldn't bother with anything beyond a basic lower keg service. It isn't even worth buying new seals. The scoring that you see under the gunk and oil is the warning. Just do a lower leg service and ride them into the ground.
Cheers everyone. Was holding air perfectly (as far as I could tell) before I took them apart. Didn't seem to be oozing. The scoring is minimal, but you can feel it. I've read about people using mail polish varnish, so may as well do that as well.
The black/lines are gunk that needs to be cleaned off.