Principally known in North America; the British equivalent is let well alone.

Bert Lance [President Carter's Director of the Office of Management and Budget] believes he can save Uncle Sam billions if he can get the government to adopt a single motto: ‘If it ain't broke, don't fix it.’
[1977 Nation's Business May 27]

If it ain't broke, don't fix it: Don't mess with a clock that runs on time.
[1984 R. Wilder You All Spoken Here 25]

The sleep pattern you have worked out is normal for you, and since you have been fairly successful in planning your life around it, why change? ‘If it ain't broke, don't fix it.’
[1988 Washington Post 5 Dec. C11]

A healthy libertarianism rubs shoulders with the ‘if it ain't broke, don't fix it’ style of conservatism.
[2001 Times Literary Supplement 30 Nov. 14]

Related to: busybodies; content and discontent

Bibliography of major proverb collections and works cited from modern editions is available here.

The Oxford Dictionary of Proverbs. Copyright © 1982, 1992, 1998, 2003, 2004 by Oxford University Press. All rights reserved.