saw an add in boating magazine for pennzoil's new synthetic blend xlf. for "seasoned" engines.<br /><br />are they getting a little crazy here? i use to use their standard oil, switched to synthetic blend, now on my first tank of 100% synthetic. is this new oil a better choice? does it really matter? are we all wasting our money? what differences could there be in their blend, 100%, and this new xlf?