[sammyg2]

There is no such thing as a perfect seal. All seals are designed to leak but the leakage is supposed to be so small that it is acceptable. Lip seals (and mechanical seals) are lubricated by the product they seal. A very small amount of oil will leak past even the most perfect lip seal and lubricate the sealing lip. The leakage can be as small as a film only a few molecules thick. If a lip seal did seal absolutely 100% it would burn up in a matter of minutes, maybe quicker.

We actually measure the amount of leakage on seals where I work, anything under 500 parts per million is acceptable. That is not very much leakage. It would take a lot of hours of run time to even make a stain at those rates.

The designers are so anal that in a pefect design the liquid being sealed stays in a liquid form for 65% of the entire width of the sealing face and then flashes into a vapor from the friction creating a high pressure zone that can seperate the seal from the shaft like a buffer and also keep the rest of the liquid from leaking out.
Darn, I gotta stop mixing work with Porsches.