Are there any secrets to removing the chain tensioner pivot bolt on a 2018 300 4rt?  So far I have tried penetrating oil, heat and a few heat cycles.  Does a steel bolt thread right into an aluminium pivot?  

The tensioner arm returns back into the swinging arm and the bolt threads in to it. There are a couple of copper bushes pressed into the swinging arm which the tensioner pivots on. They’ll probably be worn as will the aluminium tensioner.

I've just changed mine on a 315 which is a similiar set up I believe. I used a socket set with an allen key to get the allen bolt out (number 17 in the diagram above) a regular allen key just bent it was that tightly wedged in..