GMC Sierra 2500 HD rear window seal defect causing water leakage on GMC Sierra 2500 HD

Some GMC Sierra 2500HD owners report experiencing water leakage issues due to various factors, including faulty rear window seals, 3rd brake light seals, and door seals. Technical Service Bulletins (TSBs) like TSB 18-NA-383 have been issued to address specific causes, such as cracks in the rear sliding window, which can lead to significant leaks. Owners have noted water seeping through both upper corners of the rear window, resulting in damage to the headliner and electrical wires. Additionally, some users have encountered recurring leaks even after having the rear window replaced under warranty, suggesting that the problem may not be resolved with initial repairs. Identifying the exact source of the leak is crucial, as it may originate from areas like the rear cab vents or a clogged drain line on the sunroof. Prompt action, such as replacing seals and cleaning drain lines, is recommended to mitigate these water intrusion problems effectively.