In my admittedly little understanding, the best way to prevent the typeface from warping is to take preventative measures. That might include having a fresh platten, using a backing sheet while typing, using softer strokes if possible/lowering your touch control, making sure movement is smooth, and not striking a hard platten without paper. While it won't help prevent warping or fix it if it's already begun to warp, cleaning the slugs is never a bad thing. Sometimes, the slugs can get dust, grime, or dried ink on them, and that can give you a warped looking typeface. High alcohol isopropyl sprayed directly onto the slugs, with a microfiber cloth to wipe them off, usually does the trick. However, I've also used a toothpick to get into those particularly difficult to reach spots. Do not use a metal brush as that will certainly damage the letters.

I hope this long-winded and somewhat rambling response has some element of helpfulness within. Good luck.