Here is an example of a properly formatted and delimited PKCS#8 private key in PEM format. This format includes the required headers and footers:

```
-----BEGIN PRIVATE KEY-----
MIIBVgIBADANBgkqhkiG9w0BAQEFAASCAUAwggE8AgEAAkEAq7BFUpkGp3+LQmlQ
Yx2eqzDV+xeG8kx/sQFV18S5JhzGeIJNA72wSeukEPojtqUyX2J0CciPBh7eqclQ
2zpAswIDAQABAkAgisq4+zRdrzkwH1ITV1vpytnkO/NiHcnePQiOW0VUybPyHoGM
/jf75C5xET7ZQpBe5kx5VHsPZj0CBb3b+wSRAiEA2mPWCBytosIU/ODRfq6EiV04
lt6waE7I2uSPqIC20LcCIQDJQYIHQII+3YaPqyhGgqMexuuuGx+lDKD6/Fu/JwPb
5QIhAKthiYcYKlL9h8bjDsQhZDUACPasjzdsDEdq8inDyLOFAiEAmCr/tZwA3qeA
ZoBzI10DGPIuoKXBd3nk/eBxPkaxlEECIQCNymjsoI7GldtujVnr1qT+3yedLfHK
srDVjIT3LsvTqw==
-----END PRIVATE KEY-----
```

Explanation:
- Headers and Footers: The key begins with `-----BEGIN PRIVATE KEY-----` and ends with `-----END PRIVATE KEY-----`. These delimiters are mandatory in PEM format.
- Base64 Encoding: The content between the headers is the Base64-encoded representation of the private key data.
- Line Breaks: The encoded data is split into lines of 64 characters for readability, though this is not strictly required by all tools.

This format is widely used for storing private keys in PKCS#8 syntax, which supports various cryptographic algorithms.

Further, if you are still encountering problems I would suggest you try using Databricks Secret scopes.  This way you don't have to expose a key which is a security anti-pattern.

Cheers, Louis.