Dan,
  Wish I could help out a felow Iowa'n, but alass my 18/36 does not have the original seat currenty on it. My Grandfather replaced it with an old car seat with springs. The origial seat is in my uncles shead in north cental Iowa, and I should get the two together some time, and soon. Hopefully some one else here can help you out.
  What are you running in yours for engine oil? If you don't mind my asking....Kirk