F23 Gearbox Parts Info

Have just been repairing the play in my gearbox selector unit. I removed it from the gearbox to make it easier. The seal where the selector shaft enters the box is weeping oil (you can see the gap around the seal when moving the selector in/out). Does anyone know the part number for this oil seal please? Or better still where I can get one from.

Thanks.

Sorted this with an off the shelf nitrile shaft oil seal in the end. 21mm O/D x 15mm I/D x 10mm, in case anyone ever needs to replace theirs.