Subaru online parts websites could answer that.
they're benign and last the life of the transmission. they have zero failure modes and make 250,000 miles all decade long.

 

I could not find it on Subaruparts.com

 

Try subaruonlineparts.com:smile2:

 

Could not find it there either.

 

For something so small and infrequently replaced, it's not too surprising that it isn't listed on their site.

Try the direct route - call them. I would hope their dealer parts catalog is more detailed than what they put up for retail customers.

Subaru Online Parts - Hicksville, NY - 877-568-1346

 

subaru online parts lists it as "Drain Plug Gasket - Subaru (803916010)" That's a different part number from the engine drain plug gasket. No idea what size it is.

 

I got different part number. .