Posted for John Huft <aflyer@lazy8.net>:

First, quit running LOP. Try high MAP, low RPM (oversquare, like 27", 2200)
for a few hours. This is an old trick that was often used on the old chrome
cylinders to get them to break in.
 
 If that doesn't work, then when you change the oil cooler air routing, let
the naca duct pressurize the lower cowl, rather than shutting it off. That
should really screw up your cooling :o)
 
 John