Oil leak

[Marius]

My Mazda’s engine has developed a rear engine seal leak at about 60K miles. It is not a major leak (uses 1 quart every 3000 miles). Last year, in May, I switched to Castrol Syntec Blend (5W-30), and 100 miles later I noticed that oil was leaking onto the exhaust, producing some smoke. I drained immediately the Castrol, and replaced it with Pennzoil High Mileage (5W-30). The smoke was gone, but I still noticed oil drops under the car. In my case, Pennzoil HM was a disappointment. One month ago, I decided to go with Mobil Drive Clean High Mileage synthetic blend 10W-30, and as soon as I did, the leak was gone (no oil under the car).
1. Why was Castrol Syntec Blend leaking so severely? Would any group III synthetic oil leak?
2. Why is Mobil Drive Clean Blend HM not leaking? Are its HM additives more effective than Pennzoil’s?
3. If I use Mobil 1, should I expect it to leak?

 

[Chris B.]

TTT. Someone will help soon! I'd like to know as well!

 

[Pablo]

I'll just comment that sometimes seals fail "prematurely" and while one lube, fill level, drving condition may help temporarily - your engine will continue (albeit much slower in your case, due to the possible little more esters) to leak or start leaking again, sooner or later. I wouldn't blame the oils, and yes full PAO M1 with blow faster.....

I say if and when it starts again, try the AutoRx method and if that doesn't work, it's new seal time.