O-ring only seals inner pin & bushing. Outer roller on bushing is still exposed. Also you need lube for roller on sprocket interface as well. Grab roller on chain with 10K-miles and spin it, wiggle it sideways and in yaw direction and you'll find it's much, much looser than new chain. This is where majority of wear occurs; on outside unlubricated roller. In many cases of worn-out chains, rollers will actually break off, they've gotten so thin!
"Got X-miles" out of chain is super subjective with no objective 3rd-party verified measurements. What standards are used for "wear"? I can ride for 50K-miles on single chain & sprocket easily! Just that teeth will be completely worn off and chain slides over them at anything more than 50% throttle, but hey, "I GOT 50K-MILES OUT OF MY CHAIN!!!", using nothing but ground-up endangered tropical tree-frogs for lube!
Problem with letting chain wear out too much is it has lots of extra drag. Chains are 98% efficient under best conditions and easily easily saps 15-25% of power when they start wearing out. On my track bike, I use
wear-gauge and when it gets to worn part of indicator, I replace chain and flip sprocket. On street bike, I may let it go a little more than that.
Don't use motor-oil, it's designed for pressurised feed systems. Without pressure, it's not very good when parts touch each other. Use gear-oil instead, it has more extreme-pressure/extreme-heat additives and stickier. It's also what Honda recommends.
Link to original page on YouTube.
Personally, I use Chain-L #5 (has more ET/EP additives than gear-oil). Best stuff I've found yet. I've "gotten 30K-miles" out of chain with it by flipping both chain & sprockets. I drip it on rollers only and wipe off excess from outside of plates since there's there's no rubbing there anyway.
And as Drew mentioned, service interval has lots to do with longevity. I lube chain every other tank with cleaning every 4th. Track bike gets chain lube every other session and cleaning at end of day.