Leading zeros are not part of a value, but a formatting convention. To be able to retain the leading zeros, bring the value in as text.
Just because a "Number" looks like a number and is referred to as a number does not make it a number.
Example, a credit card number is 16 digits. It is not a number but an account identifier because there are not "credit card numbers" from 0000 0000 0000 0001 to 9999 9999 9999 9999.
This occurs in many instances. Part "numbers", Employee "numbers", Invoice "numbers"