My mastercraft trailer has UFP components. The oil bath bearing system is manufactured by UFP under the name Trailer Buddy. I believe the system that mastercraft used on my trailer (2002 year) is the GOLD system, not the VAULT. I like the window, it makes it easy to fill the oil and check the level. Here's where you can buy the caps and other parts. I had to order a new brake disc, and got a better deal calling them.
also some information on UFP: