I do not think leaks are related to pressure as it is to temperature. I had
a leaking core that would have the sweet smell when you first turned it on but
 after a time at operating temp it would go away. I Checked it using Ben T's
method (a tire pump and some tubing See the site it is really simple)
Could drive all day with it on and no stink. It turned out that a couple of
VERY small pin
Holes developed and would seal up when hot.

Be sure to clean out the housing when you replace the core.

Jim Morgan 86 GL "bread box"