If it ain’t broke don’t fix it

If it ain’t broke don’t fix it

and IIABDFI
sent. & comp. abb. Leave well enough alone.; Don’t tamper with something that is all right as it is. It’s fine. Leave it alone. If it ain’t broke, don’t fix it!
See also: broke, fix, if
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • loon
  • shark bait
  • lonesome
  • buzz off
  • cut up rough
  • cut up rough/nasty
  • let (one) stew in (one's) own juice(s)
  • let someone stew in their own juice
  • leave (one) to stew in (one's) own juice(s)
  • creeper