Thermostat housing with oil cooler return. It includes the mounting base O-ring seal.

The O-ring seal is not included, these can be purchased with new thermostats or on their own. The part numbers are below:
Thermostat including seal: 025-121-113/F
O-ring seal: N90-136-802

Engine fitment codes and year ranges:
DF 1.9 08/85-07/92
EY 1.9 08/84-07/89
DJ 2.1 09/86-07/92
MV 2.1 08/86-07/92
SR 2.1 08/86-07/92
SS 2.1 08/89-07/92