Step 1
Output: RawTxHex
Step 2
Output: {"hex": "SignedRawTxHex", "complete": true}
Output: Missing inputs (code -25)
Please note that, my Core Wallet is not synced so far.
Reference: https://github.com/bitcoin/bitcoin/blob/master/src/rpc/protocol.h#L46
'Missing inputs' means your wallet is unable to verify your inputs for the transaction you are trying to broadcast. This is happening because your Core Wallet is out of sync. If you wait and sync the wallet to the latest block, this would go through.
But, there is a hack to speed up this process.
1. Copy your SignedRawTxHex and exit Core Wallet.
2. Open the Electrum wallet, which you said in OP that you tried.
3. Go to Tools > Load transaction > From text.
4. Copy-paste your SignedRawTxHex and click on Load transaction.
5. Transaction window will show you details of your signed transaction. Verify everything and click on Broadcast.
You are done without syncing your Core Wallet. Now wait for your transaction to be included in a block and your coins have moved.
Fantastic!
This solves the problem I am trying to solve since July 26, 2019.
Thanks a LOT. Its a great relief to ultimately move the coins. I'll never use anything other than a legacy address ever again.