I think it might be called the water outlet housing

WATER OUTLET O-ring
90301‑40005
 
Mate if your mechanic thinks that is a thermostat housing , best to find another mechanic OMG
Have no idea where you are , but if Toyota doesnt have one you will wait about 4 weeks. I might have a spare one

Is that the coolant outlet assembly?

Yes , different shapes for different models

If its for a na motor, one dude on this forum has a few of these. Can't remember exactly who but its somewhere in the epic overheating mr2/got ass raped for 2 grand thread.

Just checked the thread. The dude is you Mandalay.

I do have spare water outlets but they are for Beams/Gen 4.
As i said there are a few designs depending on the engine but the o-rings are the same

Thanks or that, that really helps

He's runs just a small shop with like 2 workers real ma and pa sort of operation. He's my neighbor so I help him out with mowing the lawn and such and deal with the noise from the shop late at night and he helps me out with the cars. I've never seen an mr2 go to his shop so I'm sure its not the most familiar car to him I just showed him the picture I posted here and he said he was 90% positive it wasn't the thermostat gasket but since I told him it was an o ring it was the only thing he could think of that he had listed in his parts catalog.

He doesn't have the o ring so I'll have to call Toyota. It's for a 3sgte

Thanks everyone for the help you've answered all my questions