Does the Chumash Refer to the Oral Torah?

As stated in other posts, there is no technical need for the Written Torah to make any mention of the Oral Torah. We can discern the authenticity of the Oral Torah through other means, as discussed elsewhere. If we do find some reference to the Oral Torah in the Written, we can take it as a sign of God's compassion and elegance.

As far I understand, there are three rather explicit references to the Oral Torah in the Written Torah, although there are probably more.

First I will present the samples and then explain how they demonstrate the existence of the Oral Law.

The first sample is taken from Exodus 18:13-22. The background of this sample is Yisro's (Jethro's) advice to Moshe to set up minor courts.

It came about on the next day that Moses sat down to judge the people, and the people stood before Moses from the morning until the evening. When Moses' father in law saw what he was doing to the people, he said, "What is this thing that you are doing to the people? Why do you sit by yourself, while all the people stand before you from morning till evening?" Moses said to his father in law, "For the people come to me to seek God. If any of them has a case, he comes to me, and I judge between a man and his neighbor, and I make known the statutes of God and His teachings." Moses' father in law said to him, "The thing you are doing is not good. You will surely wear yourself out both you and these people who are with you for the matter is too heavy for you; you cannot do it alone. Now listen to me. I will advise you, and may the Lord be with you. [You] represent the people before God, and you shall bring the matters to God. But you shall choose out of the entire nation men of substance, God fearers, men of truth, who hate monetary gain, and you shall appoint over them [Israel] leaders over thousands, leaders over hundreds, leaders over fifties, and leaders over tens. And they shall judge the people at all times, and it shall be that any major matter they shall bring to you, and they themselves shall judge every minor matter, thereby making it easier for you, and they shall bear [the burden] with you.

The second comes from Leviticus 26:46:

These are the statutes, the ordinances, and the laws that the Lord gave between Himself and the children of Israel on Mount Sinai, by the hand of Moses.

The third sample comes from Deuteronomy 17:8-11:

If a matter eludes you in judgment, between blood and blood, between judgment and judgment, or between lesion and lesion, words of dispute in your cities, then you shall rise and go up to the place the Lord, your God, chooses. And you shall come to the Levitic kohanim and to the judge who will be in those days, and you shall inquire, and they will tell you the words of judgment. And you shall do according to the word they tell you, from the place the Lord will choose, and you shall observe to do according to all they instruct you. According to the law they instruct you and according to the judgment they say to you, you shall do; you shall not divert from the word they tell you, either right or left.

In the first sample, we see that Moses is being overwhelmed by the sheer volume of cases that he has to hear. If all of the information required for applying the laws of the Torah were written in the Torah, it should not have been so difficult for Moses to hear every case. And if we want to say that Moses was overwhelmed with the sheer volume of cases pertaining to the Written Torah, note that Moses says, "I make known the statutes of God and His teachings." Why does he have to make them known if they were already publicly revealed and written in the Torah? This is a reference to details in the Oral Law.

The second is a classic reference to the different elements of the Torah, "the statutes, the ordinances, and the laws..." Granted that some Torah commentators divide the commandments into categories, Rashi explains that, "the (plural world) laws: וְהַתּוֹרוֹת... denotes two Torahs -] one Written Torah and one Oral Torah. It teaches us that all were given to Moses on [Mount] Sinai. — [Torath Kohanim 26:54]."

The third and final sample is not actually an allusion to the Oral Torah, but is reference to the Divinely-appointed authority of the rabbi's in making legislation. The last verse in this set of verses is, "According to the law they instruct you and according to the judgment they say to you, you shall do; you shall not divert from the word they tell you, either right or left." The laws that the rabbis make are to be followed as if they were given by God. This component of the Oral Law, in contrast to information that was revealed on Mt. Sinai, is just as authoritative.