I gave that a try and "internal" transaction worked like a charm... but there's no transaction id and therefore still no goldmine outputs with txid and idx
Moving now back the exactly 1000 from my mn1-address.

Any suggestions how to EXACTLY send 1000 plus transaction fees? May it be impossible to "convert" an existing wallet to goldmine by sending initial deposit from one address existing in same wallet.dat to the goldmine-address on the same wallet?