I have one of the rollong mills you are talking about and may have a
few pointers for you.
Take some nail polish and mark the bolts. One color for the the
top bolts that hold down the gears that control the thickness of the
metal. Another color for the two smaller bolts on the side gears.
The grease that they use is very cheap the first time you take it
apart you might clean it in solovent and then put a grease with
moly-graphite. (Napa, Pep Boys or a auto parts store should carry it.)
Make sure you clean out the thread holes it will make the assembly
Make sure you keep the piece of metal you are using dry and clean
before you roll it.
Be careful not to open the roller to wide, the gears will lock up
and something could give if you put to much pressure on the handle.