That was me, just making a correction on your post.
1 Master Public Key + 1 Private Key of any of the addresses generated by that private key = can calculate the Master Private Key (aka every single private key of the wallet)
https://bitcointalksearch.org/topic/how-electrum-works-why-you-should-be-careful-with-your-private-keys-657205
Here's the original post. It kind of explains how Electrum wallets work. So OP might want to read it.
Yes, that's right Master Public Key + Private Key of any addresses. Thanks for correcting me. And this is the guy who educated me about this and made me realized how big of mistake I was making.
Thanks dabura