The seller said this was a WP 50mm extreme that came off a 525. He mentioned that these are forks that are used on various of late 90's KTM so..
I'll look up for seal that work with these forks. There is an authorized KTM dealer about 30 mins from me (Smithfield NC) but sad to say they doesnt carry inventory of bike or parts. They place order the parts you need and that's it. Another one about 2.5 hours drive is in Henderson, NC and they carry inventory on bike/parts. In this case, eBay is probably better..