Thick teflon grease is the best choice
That's what's in every toilet when it leaves the factory and the reason why toilets rarely need any lubrication for at least a year, sometimes even longer. If you want the never ending of squirting mineral oil (and btw, baby oil is mineral oil...easier to find and smells nice) into the bowl, that's ok...but it takes all of about 10 minutes to open up the pump and put a healthy squirt of thick teflon grease into it...and you only have to bother with it once a year as part of spring recommissioning.
While you have it apart to rebuild it would be an excellent time to lube it...and if you do it now, you shouldn't have to do it again till spring of 2011.
