Both aluminum and brass rads can leak. With aluminum, its often simple corrosion from using overage antifreeze or plain tap water without some sort of extra anti-corrosion additive. No-Rosion is used by quite a few Pantera owners and some shops sell rads with it included, but it doesn't last forever. A sacrificial anode is also sometimes used. So repairing a corroded rad is usually a core replacement, only re-using your tanks.
Reason is, some areas of the U.S. have tap water that's as corrosive as mild acid! I've seen high quality aluminum rads fail in less than a year in such areas. Swimming pool shops sell cheap pH test paper; if your water is below pH 7, it will dissolve aluminum. There are inhibitors in antifreeze but they also get used up fast in some locales.
Racers also have to contend with track bans on antifreeze since a crash often dumps antifreeze on the track, and antifreeze reacts with hot asphalt to produce a permanently slick spot that does not clean up. But Water-Wetter and No-Rosion in plain water are both track-accepted.
And there's more to engine cooling than simple heat transfer of aluminum vs brass. Aluminum rads have tubes that are 3-6X larger than is possible with brass rads. Those huge tubes move a LOT more coolant than brass and often fix a persistent overheat problem without changing water pumps or lines. Corvettes, Z-28s and V-8 Firebirds, besides most foreign performance cars have used aluminum rads since the '60s.