I haven't done this mod yet and have no data other than mine runs hot. In most of the pumps & boxes that I have resealed, the o-rings and seals are hard and cracked. The stock seals appear to be Butyl, it's max operating temp is ~240F, when it's exceeded the seals become hard. So cooling should greatly increase their life, along with the fluid.
This cooler maybe a case of bigger isn't always better. The fluid needs to run at operating temp, for most automotive fluids it's generally accepted to be in the 160-180F range. Cold fluid doesn't lubricate as well, is harder to pump and doesn't release trapped air as well, leading to cavitation, gowning. If you have started a vehicle in very cold weather, you have probably experienced an extreme case of this, sluggish, stiff steering and cavitation gowning when it's forced.
In a hot desert type or more temperate climate, a bigger cooler probably isn't going to be much of an issue. But in a climate where there is that nasty white stuff on the ground it could be an issue, taking much longer to warm up or never getting to operating temp.
There are a couple of ways to fix the problem; The "techie" way is to add a bypass thermostat, set at ~160F, so that the cooler is bypassed until the fluid is warm. The simple way is to mount the cooler under the hood, where it's in the airflow from the radiator fan. The cooling fan output actuality does a great job of regulating the temp, this method is used by a bunch of manufactures, ether a line loop or small cooler mounted on the front of the motor, where the fan blows on it.
