I have done some more research and the 5TA-13440-00 OEM oil filter was replaced by 5D3-13440-09.
There is some confusion on the internet with both the Filtrex OIF059 and OIF031 being quoted as the correct part e.g. some owners on a WR250R forum say use the HF141 oil filter whose equivalent is the Filtrex OIF031. Others suggest the HF140 whose equivalent is the Filtrex OIF059.
I would hate it for us to be supplying the incorrect filter!
The WR450F oil filters (filtrex OIF031) will fit, don't forget our engines are a bit of a parts bin special where they tried to use as many existing consumables as possible.
Much thanks to Totally WRs today. Fitted the OIF031 filter during my bikes first oil change. Fitted just the same as the OEM filter which i was able to see when removing. 60 mile test run afterwards and perfect, no leaks