I have to agree with Tom 100%

Typically they used to recommend that you add one quart of high end synthetic to clean out the system. Then you change the oil and filter. And then change the filter at regular intervals, but only change the oil once a year or 25,000 miles.

Now as even the Synthetics have improved, you don't even have to do that to change it over. But it's true that quality synthetics will clean out the system. Conventional oils will over time make seals brittle and the seals will shrink. This is not the case with quality synthetics. They prolong the life of the seals, and keep them pliable much longer. But if the damage is done, yes it will clean out the years of deposits and you may see more leaks because of the poor condition of the seals or gaskets once you change to a quality synthetic.

A high end synthetic is usually cheaper. Especially once you factor in the improved performance, improved gas mileage, and the longer life of the engine, with far superior protection of it's moving components. You change the oil once a year, and the filter say 3 or 4 times a year. Conventional oil you change at least 8-9 times a year and the filter at least that many times (based on the 25,000 miles a year changing conventional oil at every 3k)

The quality synthetic oils come in about any viscosity you would want. Heavier weights for hotter climates, and lighter viscosities for colder climates. The beauty of a quality 100% synthetic, is that you can use say a 0W-30 or a 5W-30 where you would usually use a 10W-40 or a 20W-50 weight oil. The motor produces more HP, the motor pushes the oil easier and more efficiently, and all this with superior protection. So you can use any viscosity you want in either conventional oils or quality synthetics.

This is why in the last 5 years every major oil company has all of a sudden come out with Full synthetics, synth blends and the like, as well as in the last 10 years there are at least 2-4 additional companies who have come out with 100% synthetics, not to mention the pioneer synthetic brand that has been around for over 25 years. Yes, most of the shows you see also praise the benefits of a quality synthetic lubricant. Not just the oil, but gear oil, tranny fluid, antifreeze etc you name it, and it's out there in synthetic form, and will out perform it's conventional counterpart.

Now is it right for everyone? No, like Jim said, if it isn't broken, don't fix it. And some of out car are not driven that hard or especially that often. The fluids get changed more often than needed etc... so it would not be a huge benefit for many of our birds for example.

For me, I saw the benefits early on, and did the math for myself... and I know that many of my cars would never have seen 250,000 - 315,000 miles unless I had switched them over to a high end 100% synthetic as soon as I bought them. All my cars are used, and who knows how well abused before I got them...

So if it leaks more, it's because the problem was there before, and plugged with sludge and build up.. now that it's clean, the poor seal is just that, a poor seal. Synthetics will in most cases help recondition the seal, but only so much...

Yes, I've done a LOT of reading up on both sides of the issue... and even between brands of Synthetics, and yes... there is a big difference.

Just my opinon... but I feel better using it than I would using conventional oils.

Brett - 67 Drop Top 455! (sorry for the long post!)