If you use the key more than once then it isn't a One-Time Pad. It's one step above a substitution cipher, and if any of your unencrypted private keys ever does leak, so will the encryption key. It's possible that someone more experienced with cryptoanalysis than myself could even derive the encryption key from multiple encrypted private keys. The whole point of a OTP is that you use one bit of unique, never-used-elsewhere entropy to encrypt each bit of the message. The fact that each bit of the pad is unrelated to anything else the attacker might know is what makes an OTP resistant to cryptoanalysis.