Both ball bearing and floating bush bearing systems still have to retain oil within the CHRA (negligible amounts can seep) but there are a lot of reasons why oil can leak from the bearing housing into the end housings, none of which are manufacturing related......unless of course we "forgot" to put the piston rings / seal plates into the CHRA on the assembly line.
Some applications are prone to problems due to the installation conditions or because of the other engine parts which surround the turbo. For example, if the crank pressure gets too high you get oil leaks. If you block or restrict air through the air filter you get an oil leak, if your oil pump is pushing too much pressure....guess what happens?
Turbos leak oil or fail for a reason, if you don't investigate the reason then repairing / replacing a turbo would be pointless as you are highly likely to see the same problem happen again in a relatively short time.