Purity: Doubt After Wudu Regarding a Known Obstruction
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 294:
If before performing wuḍūʾ one knows that on some parts of the body on which wuḍūʾ is performed there is an obstruction for water to reach those parts, and after wuḍūʾ he doubts whether at the time of performing wuḍūʾ he made water reach those parts, his wuḍūʾ is valid.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)