Why I'm rebuilding my engine
 

I have a 1991 C2 coupe 911 I bought 3 years ago. After purchase I noticed alot of oil leaks. I changed the oil with Castrol GTX 10w-40 and noticed the leaks slowed down. I slowley fixed all of them with seals, gasket, o-rings etc. with only having to do a partial engine drop. I ended up with one oil leak that droped 3 drops while cooling down then stoped. I was very happy with that.

I heard alot about Brad Penn oil so I thought I'd try it. I bought 2 cases of High performance 10w-40 and immediately after the change I noticed my engine was leaking out of many areas and the one I mentioned above became bad, rel bad. I then read the oil bottle and it read "partial synthetic".

Now for all I know it might not have anything to do with the oil change and maybe a coincedent. Needless to say I am halfway through my engine rebuild and I'm glad, because it was in need anyway.

I don't have any history with Castrol, but after break in I put in Brad Penn 20w-50 in my 3.3L and no leaks so far...your issue could just been a coincidence or maybe it was the weight...any chance you overfilled it?

Thanks for your response. I know I did not overfill it but would overfilling it cause new or worse leaks. As far as weight, I live in a somewhat cool area. Do you think I should use heavier weight anyway?