Rip Trippers did a good video about these things and rebuilding them. If you are into trying that it is very helpful. I noticed a huge change in them after doing this method.
https://www.youtube.com/watch?v=pwgkYUgZXHI
Also I modified how i rebuild them to this method. It is a bit advanced and should not be done unless you are into tinkering. Also it changes the head from a dual coil to a single coil.
Take the head apart like he shows in the video
1-once the head is apart toss the little filler material that goes between the cap and cup
2-toss the insert that goes between the coil and the cup
3-take a 1/32 drill bit and made the two stock holes bigger (do this while the cap is off the unit so you don't damage the inner guts)
4-wrap your coil and reinsert it into the cup and reassemble it the way he does in the video up to the point of putting the cap back on
5-roll a cotton wick that sticks out about 3 inches on each side (this method does not work with silica)
6-screw the cup into your tank base
7-insert one side of the wick through the hole and then insert the other side through the other hole
8-prejuice the wick you do not want to dry burn the cotton or it will actually burn
9-slowly lower the cup while carefully pulling the cotton through
10-turn the cup about an 1/8th of a turn and then press fit it onto the cup
11-flip the whole thing over and press it against a hard surface to fully seat the cap on the cup
12-trim the wicks to about 2mm outside of the cups
13-fill your tank and put everything back together let it sit for about 10 min take a few primer puffs and you are good to go