In the future, you never really have to replace coil sleeves unless they're physically damaged. You can squirt some Novus 2 on a rag, work it into the sleeve, and twist it around to really clean it out. I've also soaked them in hot, very soapy water.
They're cheap and easy to replace, but nobody can tell the difference between a cleaned one and a new one.
I've done this in a pinch, or for friends pins to get them working. I would never do it on my own games though. Old sleeves will get brittle and have scratches in them that will quickly refill with gunk.
Replacing sleeves is just a good practice for longevity, especially on high use coils.
As for your rebuild, those sys. 11 cabs always have bad pitted flipper switch contacts. There is an easy way to diagnose it.
If they seem weak when you are playing a game, try gently but firmly pressing in the button instead of smacking it. If this makes your flipper strong, you have worn switch contacts. Usually you can see the spark through the shooter lane gauge when you slap it on worn contacts.
I did a rebuild on a Comet and it had little to no difference. It's better to only do a rebuild if something is broken in the mechanism, or if a disassembly and cleaning doesn't fix the problem.