Best if you can get the saildrive cleaned off and then primed and antifouled with aluminium friendly paints. My saildrive has had cruiser uno antifouling on it and was looking a bit pitted in places. I've since cleaned and filled the pitted areas with a two pack epoxy filler. Now I always use aluminium friendly paints on the saildrive. For the paint removal you can use a paint remover followed up with a rotary wire brush, or just the rotary wire brush on its own, but remember to protect your eyes from anything that gets thrown off, in particular pieces of wire from the brush. Then wash it all off to remove traces of paint remover, allow it to dry and then apply primer paint. Don't paint over the anode or the area where the anode contacts the aluminium casting of the saildrive leg. If you use a spray primer it should dry very quickly, but pay attention to any temperature restrictions. Some paints recommend they should not be used below 10 degrees C., which can be a bit limiting at this time of year.