I am currently replacing the head gasket on my 300e 103 motor, the head is back from the machine shop, have all the parts to put together, gasket set, headbolts etc.. an old school mercedes tech told me to apply permatex hight temp sealant on the edges of the head gasket,I work for a honda dealership as a technician and hve done many head gasket replacements but never applied any sealant on the gasket surface, dont know wether to apply or not , mb techs please advise! also when looking down the right side (driver side) chain rail, there is an O ring wedged between the rail and the block, dont know where it came from, not planning on replacing the chain or the guides but I heard a slight pop when I was pulling the guide rail pin when using the mercedes special tool, did not continue and backe it out right away, instead pulled out with slide hammer.Inspected the rail, and found no visible cracks. Mb techs please help with your expertise!