the cylinders is oiling them.There are also spray can of fogging oil you can find in automotive sections.If the engine has any leaking seals.Synthetic would make it leak even worse.I personally use synthetic oil in almost everything I own.Even my shop air compressor.I wouldn't consider synthetic cost effective though for people who trade cars every few years.I rarely ever sell or trade my cars.I usually drive em till they drop.And deffinitly change those valve stem seals.Can't help with the plug gap.If nothing else,call the local parts store.The gaps are listed in the spark plug catalogs.