Will Synthetic Motor Oil Cause Engine Seal Leaks?

Is it true that synthetic oils will actually cause harm to the seals in an older engine, causing it to leak engine oil? Project Farm tests conventional Shell Rotella T4 15W-40 and full synthetic T6 5W-30 oils in a Ford 5000 tractor that’s forty-five years old and has never tasted synthetic oil.

So, let’s put some synthetic oil in that tractor, put to some hard work and then come back and see if the engine is leaking oil…