I downloaded the Dichtomatik seal catalog today and had a look for the 475PTO side seal.
Size to look for is 17mm X 35mm X 4mm (3000FPS)
http://www.dichtomatik.mx/catalogos/Dichtomatik_Catalog_2012.pdf
They have two nitrile seals that may work. They have the rubber coating on the case which wraps the end according to their pics which possibly could be sanded back to get to 4mm. Page 74 in the catalog
17X35X5SC (5mm depth, single lip)
17X35X5TC ( 5mmdepth double lip)
Tim I looked at my notes and the actual size of the seal is 17X35X4 mm single lip. So it is very possible that one of those seals that you have listed could be ground down to the required 4mm thickness and could work. Thanks for the info.
They are Partner design by the way I think.