sorry for being a little slow to reply. since I usually utilize Hipshot tuners, I wanted to do a little research before answering
here's what the Schaller website has to say about stiff tuners
(since it's difficult to read, the Q is:
After several years of use my machine heads are hard to turn; what can I do?)
you can also reference the tuner schematic parts drawing here:
http://bass-machine-heads.com/download/ ... 3aff42X3a7 if you look at the bottom and top views on the pdf you can see the plastic washer between the mounting/retaining plate and the threaded gear nut (though it's not directly called out with any text)
my initial thoughts were to add a minute amount of lubricating oil to the tuner, and the Schaller on-line FAQ confirms this. I would avoid WD-40 (or any other kind of silicone containing lubricant) as it will contaminate your bass in a way that causes significant issues should you (or a future owner) ever decide that there is need to refinish the neck
all the best,
R