The brake cleaner would remove any grease that's lubricating the screw. The WD-40 is not a replacement for it. Ball screw nuts typically have wipers on them that prevent dust from entering the ball race, but it's possible for those to fail. If simply re-greasing the screw doesn't make it work better (which it might) then removing the whole assembly, disassembling it (carefully saving all the balls, checking them for damage, and replacing them if necessary), cleaning and reassembling (replacing any damaged or missing wipers), then replacing the grease (without mixing it with anything else) would be the alternative to replacing the whole thing.