Does your MC leak like this? What brand MC's have you all had luck with?

 

no, they're not supposed to leak at those seals.
does yours have a lifetime warranty, if so just return it for replacement. if not, i'd recommend a Advance online buy, pick up in store with i think? ES123 discount code ($20 off 50) so it costs you about 30.

i doubt that air is getting into the lines through that leak, but brake fluid is nasty corrosive to paint, so its best to fix it. those seals are in the reservoir, so any air getting in should just perk up to the top, rather than get into the piston and lines. an air leak into the lines would be accompanied by a high pressure leak when mashing the brakes. mashing- that's a technical term...