I wrote them a letter cause I wanted to know, if switching to syntec after conventional can cause leaks and here is the answer.

A quality synthetic motor oil can be used in old as well as new cars,
including cars in which conventional oil was previously used. While
using a synthetic motor oil in newer cars has been well documented, Castrol
SYNTEC also provides added protection through enhanced seal compatibility-
which is extremely important for used cars. Therefore, synthetic motor oils are
beneficial for the good health, long life, and top performance of new
and old cars. And any consumer looking to get the most out of their car
should consider using a premium Synthetic motor oil.

Castrol SYNTEC full synthetic motor oil will absolutely not cause a
leak in a high mileage engine. This is a common misconception.

However, although a synthetic will not cause a leak, it could
potentially find one in an engine that has a pre-existing leak. In fact we don't
recommend switching to a synthetic oil especially if you are already
experiencing a leak, because it will make a leak more apparent.

This is because Synthetic oils contain 'Detergents' that will
immediately begin to clean away any sludge or buildup in the engine, particularly
around the seals where sludge likes to gather. Detergents help your engine run
clean and cool and therefore efficient. If however, you have any
damaged seals currently blocked by this sludge, a synthetic oil will wash the
blockage away and make an existing leak more apparent. This should not
be a worry if you have a well maintained engine. The sooner you use a
synthetic the better. Many vehicle manufacturers use Castrol Syntec in there new
cars and trucks right off the line.

There is also the option of GTX High Mileage, a conventional oil with a
special additives package that benefit engines over the 75,000 mile
mark.

 

nice formating.

 

fuck if im gonna read that haaaaaaaaaaaaah

 

I think it works well with the context of the explanation.

 

i ruined an engine switching to sythentic.......crap I tell you, crap!!!

 

As far as the formatting goes I guess I can fix it. I just cut and paste the email and that is how it came out.

 

I'd rather run dino oil and change it more often.

 

I'd rather run synthetic and be a lazy asshole.

 

id rather run synthetic and be a

o wait

 

I change my synthetic at 15k miles now... no reason to change sooner h: