Originally Posted by jyasaki
Most of the ones in the US have a polycarbonate cap that may crack/shatter if thumped, which will cause a bit of a problem.
as are mine, which means you can see the state of the oil at a glance at any time - so rather than maintenance free it might be better to say incredibly easy to keep an eye on rather than the usual blind hope. I've read other people worried about the plastic cover getting bumped - I think you'd have to be quite unlucky but its probably possible to engineer a protective cover.
I think trucks and busses often use something similar here.