Originally Posted by dirtysouthjacket
2 Reasons, it makes it easier to remove the next time and prevents O-ring failure. The o ring will be dry and "could" freeze to the surrounding metal. It can cause the o-ring to stick to the filter or engine case and make it a lot harder to remove the filter the next time. I had a friend have this happen to his boat. Once he finally got the filter off (which was apparently a PITA), he didn't check for the old o-ring. It was stuck up on the engine where he couldn't see. He put a new filter on with a new o-ring, which then resulted in the new o-ring AND the old (or whatever was left of the old) o-ring being between the filter and engine. Ended up blowing out one of the o-rings, lost all the oil and seized the engine.
Regardless of the engine type, I've always checked to make sure the entire old o-ring comes out and that the new one goes on correctly and is lubricated with oil. Its probably just going the extra mile and won't always cause failures, but not a lot of extra work.
Don't get me wrong I do it every time...... just never bothered with coating it in new oil.... working at a dealership I've had days where I'll do a dozen oil changes in one day and the process involves draining the oil. new filter and then grab the jug of new oil before filling the bike. So old oil is just fine to coat the new filter ring