Where do countries under international sanctions find spare parts?
The consequence of sanctions on Arpartheid South Africa was a thriving military equipment sector with some remarkable products, including nuclear weapons. Simply put, other people are clever enough to find equivalent solutions to US engineered parts and only when a super expensive fab costing billions is needed will they need to downgrade their specs. But don't think that sanctions will in the long term keep other countries from owning fancy equipment: They will learn to build it themselves.