jamie taylor

In addition to the above thorough answer you could if your option is to run on unleaded until your seats need replacing use a product called Flashlube.
It drip feeds in through the vacuum of your inlet manifold and lubricates your upper engine.
The Aussies have used it for years especially when running their cars on LPG as I am also running my car on LPG and no new hardened seats. I belt up and down the motorway once a week for the last six months and the 30 year old engine has only improved so far.