In the 1980s, China sold DF-3 ballistic missiles to Saudi Arabia. The agreement included not only the missiles but also services such as base construction, training, operation, maintenance, and operational advisory services.
The Second Artillery Corps (the predecessor of the PLARF), under the name "Golden Wheel Project Company," established military bases for Saudi Arabia and deployed troops there on rotation.
The above information is publicly available.
Logically, the "Golden Wheel Project Company" was a special, temporary organization established specifically for Saudi Arabia's ballistic missile program. It should have been disbanded after completing its mission.
However, in reality, this organization still exists. Although it is a highly classified organization, we can occasionally glean clues from news reports. It is directly led by a PLARF major general and reports directly to PLARF headquarters.
So, can you guess why this organization still exists?