I always used to think that synthetic oil was expensive and would make
anything leak.   I tried some about 15 years ago and soon changed back.
However after a recent experience in my '91 Carat I am no longer sceptical.
I changed oil just before heading to the mountains.   Castrol 20-50 to Mobil
1.
About 5-10 miles after leaving home , the temp gauge was where I had become
accustomed to seeing it.    Then, the needle started dropping .....and dropping
over the next 50 miles.  Nothing dramatic but noticeable.     It now stays
about 3/16" lower than it did before.
I was wondering if there was anything else that I could have done to make
this change but no, I dont think so.   All I did that morning was change the oil.
I had a slight water leak before and I still have one but I didnt even add
water before leaving.   It sure made a believer out of me.      Mobil 1 15W-50
from now on !

Steve Cotsford
Columbia SC