According to the Factory Service Manual the Engine has to come out & be at least partialy torn down & it references a Special Seal installation tool,Might want to ask over ay Polaris Forum I am sure there are some folks overthere with 1st hand experience
http://www.polarisatvforums.comHere is a detailed post on the seal on Highlifter forums with out engine removal or tear down
http://forum.highlifter.com/m3206595-print.aspx