On the dyno I found that my original heater control valve is leaking through the diaphragm. I am not finding a good source for the valve for 1970. I found some real old stock new ones but worried that they may leak also? Is there an option for new ones that at least have the same angles and the vacuum works them the correct direction? Maybe I will have to chance an old stock one?

 

Chance an NOS one
there is one f/s around here for $25

 

Rock Auto shows FOUR SEASONS Part # 74601

Is that not the correct heater valve?

 

Yes it is. It is the same thing you will get if you order a valve from any of the Olds supply houses.