Everyone is right so far. Sheffield is one of many companies that buys generic knife and tool designs from China, slaps their logos on them and resells them. It's not a super high quality tool over all, but if you get a decent one, some can last for many years.
Taking it apart will likely involve drilling some rivets out and replacing them, which I don't advise. WD40 and some brushing (as mentioned above) is likely your best bet. You can also try using some unwaxed dental floss to clean out the pivots. When done I usually use some dry lube like powered graphite in the joints to help loosen them up.
Def