When Would It Leak After Switching to Synthetic?
 

I'm about ten days and a few hundred miles into a switch to Mobil 1. Last oil was a blend, dino before that, AFAIK. If leaks were to appear, would it be right away, or does it sorta depend? FWIW the 3.0 engine has +100K on it, and had a top-end done ~8K ago. It didn't leak before (after the top end, that is), and I haven't seen any leaks to this point since putting the Mobil 1 in.

Also, is a 911 more likely to leak over time with prolonged synthetic use compared to dino?

After reading lots of posts about motor oils in older 911s, and synthetics in particular, I decided to try an expensive experiment on my end-of-summer oil change. My 1983 911SC has over 70k original miles and the motor is unmolested. I had previously dropped the motor and replaced every seal, O-ring and gasket where leaks normally occur. With 15-50W dino oil, my motor was dry and my oil consumption was 1qt/800-1,000 miles.

Shortly after adding the Mobile 1, I saw smoke from my headers, drips on the bottom of my motor, and oil spots on the garage floor. I ran it for a while, enough to get an oil consumption reading, and was down to needing a quart after 500 miles.

I decided to dump the expensive stuff and did a change back to dino oil with a new filter. Now, with about 1,000 miles on the fresh oil, I need to add a quart. I still have some wetness on my motor, but the dripping seems to have eased-off. My headers still stink a little, but I'm not noticing a cloud of blue smoke around the butt of my Porsche when I'm stopped.

I don't know if this helps, but I won't go back to synthetic until or unless I do a motor rebuild and have all fresh seals on my motor.