I bought the paper gasket along with the filter. But the next time I inspected/cleaned the filter I used red RTV sealer in place of a paper gasket. You just need that cover to not leak oil, nothing fancy. Its not under pressure, its just an oil reservoir.
Wherever Yanmar used an o-ring for sealing, they intended it to be re-used. Whatever you find there, just re-use the o-ring or replace paper with RTV sealer.
As I learned, and noted above, that internal o-ring around the middle of the filter that separates the sump side of the filter from the cleaned oil chamber is more critical. For that one, it is worthwhile to order the correct part to use at the next filter inspection.
I had forgotten: As Winston pointed out there is an Early and Late version of the filter screen, and also Early/Late inspection covers. Including the tractor Serial Number when you order parts is a good idea.
Like the reusable o-ring here, the valve cover gasket is made from sheet rubber and is intended to be re-usable. Yanmar put a lot of thought into making these easy for the owner to maintain.
Re the Hinomoto - is it listed in
Tractordata? Some of the small Massey Ferguson models were rebadged Hinomotos so you might find it is well supported. And they were certainly respected as a top quality brand. I might take a chance on it - with the expectation it might cost some money to get it running.