A long time ago in a universe far, far away I owned a Vauxhall Viva. The 1200 cc engine was notorious for forming mayonnaise (emulsified oil and condensation) in the valve cover with the green gook very apparent on the oil cap when you took it out. If you ran only short runs it would block the breather hose to the carb. Vauxhall (The British Division of GM) came up with a solution.
They issued a diagram of a plate to be made/fitted by owners to block airflow from the engine driven fan across the valve cover. This allowed the cover to get much warmer and cured the problem.
I wonder if replacing the engine driven fan, even though it has a thermal clutch, with an electric, thermostatically controlled fan would help or solve the problem?