of course Germany would never willingly allow the Soviets near the Romanian oilfields, the OP is unclear on when this occurs, if it is during invasion of France then Germany would have few options to stop them.
And, again, why would such a cautious man like Stalin invade Romania despite not first formally agreeing with Hitler? Like he was thinking Hitler was like: "The Soviets start an invasion without notifying us first, their allies, and while we are busy with the invasion of France. Nothing strange." Even when he started to invade and occupy Eastern Europe in 1944, he still had to agree with Churchill how much he would influence those countries (altough he only wanted to formalise his ability to influence, not it's limits), and those were countries that started the war first. As I said, as cruel and bloodthirsty as he was, Stalin was always extremely cautious, because he knew that both Hitler and Churchill did not saw him as a true ally, but as the lesser of two evils.
agree with your projected division of Romania, have always wondered if Germany and USSR had left Finland and Baltics out of their agreements but dealt with Romania (as they had defensive agreement with Poland)
I think that Stalin saw both Finland and the Baltic states as better second and third targets, because Romania, like Poland, also had defensive pacts with France and Britain and who knows? Maybe King Carol II could better convince the British and the French to launch a Second Saar winter offensive? Hitler wouldn't like to face a maybe "true" offensive, just because Stalin can't wait to settle the score with Romania until after he would deal the death blow to France. Also, who knows, maybe not wanting to look weak in front of their people for failing to defend two of their allies from the Soviets and the Nazis, the Allies would even bombard the Caucasian oil fields?