Very true. In fact, if your lathe does have sealed bearings, there is absolutely no point spraying them with anything, since it won't get inside if the seals are OK, and if the seals are broken you need new bearings. By all means, spray the bed, the banjo, the tool rest, and whatever other parts you like with a protective oil spray (NOT WD40) if you want to keep any rust off, but leave the motor and the bearings alone.