Quote Originally Posted by 98lee View Post
Leaks are caused by the condition of the seals. Slippery synthetics are less forgiving of hardened seals, but the oil doesn't CAUSE the leak, bad hardened seals do.

Higher mileage is actually better for seals than just sitting for years.

Choosing oil based on leakage vs performance is not the choice I would make, but each person has their own priorities.
You are right. Synthetic oil doesn't CAUSE the seals to leak but they do ALLOW the seals to leak. It didn't matter to me why they were leaking, it only mattered to me that they WERE leaking.

I considered the choice of oil based on leakage vs performance and I had the following choices:

1. Continue to use synthetic in my K bike and let the rear seal leak so it would drip on my garage floor and possibly get on my clutch.

Continue to use synthetic in my Airhead and let the pushrod tube seals continue to leak onto my garage floor and motorcycle.

2. Continue to use synthetic and spend hundreds of dollars having the seals replaced on both bikes.

3. Change to conventional oil, have the leaks stop and ride for many troublefree years.

I chose to return to using conventional oil. I sold the drip free K bike a year later and I have had my drip free Airhead 14 years since I changed back to conventional oil.

I'm not against using synthetic oil if you want to do so but I'm just saying if you do and the seals leak, you may save money and aggravation by switching back to a conventional oil.