Yes it is 100% OEM supported.
US has not halted Pakistan's F-16 sustainment program due to strong protest lodged before buying the Block 52's back in 2005. And trust me when I say this, the guys at Lockheed were embarrassed. Their lobbies work in great favor for Pakistan in Congress to date. Some written agreements were also signed back then for continuity of sustainment program as long as Pakistan was not blacklisted or earns the status of a 'failed state'. There is a reason why keep spotting our C-130's at Denver AFB, embargo or not.
The air life is a highly classified information. We cannot know for sure if it is 25% or 50% in this point in time.
However, the best I know is, we are good to go for the next 15 years on average before the first of the missiles come close to the 1800 hrs mark. This calculation takes into account full scale standoffs with frequent CAP times.
US would sell Pakistan F-35's if we had the buck.
When Congress puts embargo on Pakistan and halts such contracts, it takes a toll on US jobs. And they dont want to lose their seats in their home states.
The Zulu's are coming. Whether you like it or not.