Any tips on installing a block heater on a '90 420SEL? I am about to do this tonight or sometime this weekend and woud like some input. I already have access to a 19mm allen socket that was fabricated for this purpose. Any hints on removing the plug? I hear it is a ***** to get out. I am flushing out the old coolant (less than 6 mo. old but the local indy put in GREEN coolant) anyway so thought this would be the ideal time to install one. Any danger of damagine the block when taking out the old plug?