It's called a "bleeder" valve 1st of all.The reason it's there is to bleed out the air and water that build up over time and even to bleed out old brake fluid from a car's system.It's always done if the brake system was ever opened,meaning changing a brake line,a caliber,a wheel cylinder in the case of older cars with drum brakes and if the master cylinder was ever changed.But NOT if just the master cylinder was opened to check for fluid level.If the bleeder valve is leaking,I suggest one of the following:
- 1:If it's leaking around the screw itself where it goes into the caliber,tighten it to see if it's a little loose.DO NOT OVER TIGHTEN.
- 2.If it's bleeding from the tip(it works just like the valve stem on a tire and acts like a check valve keeping the air,in this case fluid,inside and air/water out),you're may need a new valve.However,sometimes a very small particle of dirt may get inside the tip and cause the valve to stay slightly open resulting in some loss of brake fluid and the intake of air.Everytime you step on the brakes you will lose brake fluid and take in air.In the long run,the pedel will end up going to the floor and you won't have any brakes because there isn't any fluid.
- 3:If you do #1 becareful not to strip the threads out of the caliber.If you do,then you're going to need a 'Helicoil' which has threads on both the inside for the Bleeder valve and outside to screw into the brake caliber.Once the Helicoil is installed,the bleeder valve can be screwed back into the caliber and makes it as good as new.
Since you said that the caliper is new, if it is defective you should return it for a replacement before the warranty expires. As this type of defect, if it really is defective, does not appear until the caliper is installed and the brake fluid is refilled, you should be able to get another caliper at no charge.Whatever you do, don't try to repair the caliper yourself if you can exchange it.