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2015-2023 Mustang Shrinking Quarter Window Seal Guide

Created by Andrew Perry / 2 min read
Date Created: 8/22/2025
Last Updated: 8/22/2025

Check out our quick guide for fixing the infamous shrinking quarter window seals on your 2015-2023 Mustang!

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Viewing this install and using the information shared is subject to the terms set forth here - View the LMR Install Instructions Disclaimer.
Over time, the rear quarter window seal on 2015-2023 S550 Mustangs can shrink, crack, or fade due to prolonged sun exposure and age. This is a common issue caused by UV damage and heat cycles, and unfortunately, Ford does not offer the seal separately; you’ll need to replace the entire window assembly.

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What Can Cause This To Happen?

  • Sun exposure causes rubber to dry out and shrink.
  • Age and weathering lead to cracks and fading.
  • Minor impacts can damage the window or seal.

What Does This Do To Your Mustang?

The rubber weatherstrip around the rear quarter windows begins to shrink, dry rot, or pull away from the body of the car. This leads to a loose or gapped seal, which can cause:
  • Water leaks.
  • Wind noise.
  • A faded or worn appearance.
  • Potential glass loosening over time.


How To Fix This Issue:

  • Replace the entire rear quarter window assembly (includes seal).
  • Remove interior trim panels.
  • Unbolt and remove the old quarter window.
  • Clean the area of old adhesive/debris.
  • Install new OEM window assembly.
  • Reinstall trim.
2015-2023-mustang-s550-how-to-fix-shrinking-quarter-window-seal_6258d452.jpg (800×800)
This issue can be just cosmetic at first, but it can turn into a safety concern if left unaddressed. Be sure to check out all of our other S550 articles and guides for more information on the 2015-2023 Mustang!
Thumbnail image of the author of this article, Andrew Perry.

About the Author

Andrew has been writing content for Late Model Restoration for over 2 years, producing over 50 articles. Over the years, Andrew has owned numerous Mustangs, including a 2007 V6, 2003 GT, 1967 GT, 1994 GT, 1995 GT, 2014 GT (2), 2000 V6 (V8 swapped), 2016 GT/PP, 1988 LX 5.0, and a 2009 GT/CS. Read more...