Originally Posted by Poly
I've got oil bath hubs on my trailer which is now something like 8 years old and never had a bearing change... I'm probably going to change the oil this year. They are reasonably common across the atlantic - especially on smaller trailers.
Was going to say that they're not really new... You beat me to it.
AFAIK, they're not really "maintenance free" in the sense that they don't require any looking after; they may still leak at the inner seal and may require top up now and again. 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.
All the above is from reports; I have standard roller bearings on mine. Not all that different; just that the oil is suspended in soap and released when needed.