Never use white grease to assemble a motor ,especially if it will set for any length of time ! Nicks heads were rebuilt about a year ago ,the shop used white grease and it hardened ,it leached into the valve seats and was a pain in the butt to clean out . The valves were stuck in the new bronze guides . A bit of cussing ,a bit of brushing and 2 cans of Chem tool and the finally cleaned out . Going to give the valves a light lap and reassemble .