Just got out of the house and did it to mine, also. I sprayed with the fan off, using the thin straw from WD-40 spray can. Then i started the fan for a few seconds, stopped and sprayed some more.
So far it seems to have worked, but i will wait until tomorrow when it will be frozen again (-20*C announced tonight
ps: mine also had the rusted bolt in the center, although i noticed it had some sort of 'cover' over that part (probably to avoid water from pouring directly on the bolt). Don't think the actual bolt is the problem; more likely the motor shaft/ shaft sleeve + slight rust on them.