This level sensor lives in the coolant pressurized expansion tank in the engine compartment of the Van.
Fits water-cooled Vans 1983-1990 (1990 up to chassis # ending in 030333).
This unit includes the O-ring.
You can find a new electrical connector for this version of sensor here: Coolant level sensor connector
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If you are a 1990 (from chassis #030333) or 1991 Van you need the sensor at the link below:
1990 - 1991 Coolant Level Sensor
Ref ID: 251919372