Do you think that that is really true about being able to leak more so ,synthetic, over conventional? I went to one of those Quicky lube places with one of my crashers as I didn't have the time to do it myself and a lube Jockey told me the same thing. I just gave him the stink eye like OK what-ever!
I myself don't see it 5w is 5w synthetic is a better long lasting lubricant I just don't see how it will slip through the cracks easier. All oil when cold has a different pour characteristic. Is there any real proof,doubting Thomas here?
I know that when synthetic is placed in an engine that has run dino for a long time there is a chance that oil will be consumed at an alarming rate with no apparent external leaks. I saw this with my fathers 6.0 gasser. I think he had about 135k when we tried to make the switch.
It would also make sense to me that there would be a chance for older seals to not be able to contain an oil that is more slippery. I agree, 5w is 5w, but there is a difference in pour point temperature between oils with the same weight. I'm not saying the seals are damaged by the synthetic, simply that older seals that have wear may not be able to contain synthetic where they would still be able to contain a dino oil. I have also seen SBC's that were switched develop valve cover gasket leaks with the synthetic where there was no visible leak with the dino. We changed the valve cover gaskets and no more issues.
I'm not trying to frighten anyone off here, just saying what I have seen, in specific cases.
FWIW, I love the synthetics, and run them in everything I have except a HIGH miles '97 Suburban I bought well used for the kids. The sub and dad's truck get dino.