An 18 word seed could/should be BIP39/BIP44? As per
https://iancoleman.io/bip39/You could try this tool ->
https://github.com/iancoleman/bip39 (Always run this offline!)
I have 18 words seed "spray inject ... ... ... "
And i have some password/secret key or private key "GVzPYhu............................" (35 letters total)
35 letters sounds like it's an adress - not a private key, but even then, the prefixes are all wrong.
Might it be the adress prefix of a specific altcoin?
Gulden for example uses "GZaubDd2cadyyoc5UB2ZEwdFxSivybnUVD" - the same prefix.