Sounds like a good tip and as I have the cork gaskets already cut, I think I will go along with your suggestion and see what happens.
A big thank you to you guys that have helped me out. N.Z. is a long way from U.S.A. and it can be a bit lonely out here when it comes to A.C. tractors. There is no A.C. agents and most of the people I speak to have never heard of the make.
I am very impressed by the way the forum works and with the replies received.
Once again many thanks