I wouldn't put seafoam in anything. I would contact high performance lubricants and see if they have a recommendation for your application. if you hear nothing from them I would call BG or Liquimoly and I'm sure that they would have a suggestion or a product that you could use. onto a simpler yet more time consuming effort, I would recommend that you try a high detergent oil like red line but I don't think doing that quite yet is as important as just getting a bunch of oil filters and some oil and changing it out a lot. I would though recommend the red line fuel system cleaner for its high content of pea and my hope is that if you continuously run that in the gas tank that eventually it'll run down into the oil and slowly start to work some of that stuff free.
Lead Substitute
Prevents valve seat damage in engines designed for leaded gasoline
www.redlineoil.com