[mb1]

Yes, I've heard of the two challenges you've cited.

1. if air or dirt enter the system its a very expensive problem made worse by attempting to change the fluid and pan.
2. If you don't remove the pan, you only get 4.5 -5 ltrs out.

My thought would be that it would be safer to change it more often even if you only get 5 liters out at a time.

If we find that the fluid is broken down at 30k or 60k like I expect it to be, maybe it would make sense to take 5 liters out and replace fresh every 30k miles.

If someone can validate based on oil analysis, I know I'd sleep a lot better.