Basically, you can open up the wallet file with anything that can display hex (like Sublime Text), and then search for the following 4-byte pattern: 4300 0130.
I am not the most familiar with wallet.dat but it looks like the 0x43000130 should be considered a variable even if it appears similar for everyone. For example 0x30 (=48) is the length of the encrypted key, and 0x43 (=67) is the length of the total structure.
The actual fixed starting bytes that should be searched is 0x090001046d6b6579 with "6d6b6579" being hex format of "mkey" and "04" being its length.