Thermostat housing without the oil cooler return. It includes through 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:
DG 1.9 waterboxer 08/85-07/92
SP 1.9 waterboxer 09/86-07/89