Yes, it is, but it can be done. Be careful not to over torque to get it to opened. Those gears (teeth) can strip and I think replacements are a little hard to come by.
I took mine out of my '39 and bench checked it for chips and lubed it. Put it back in and it worked great.
Remember it's been doing its job for a very long time. It was Henry's idea for a "defroster"!!