The Rambam (Hilchos Mamrim 1:3) writes: There cannot be an argument regarding a halachah learned from a Halachah l’Moshe mi’Sinai. The obvious question is from our Gemora (Bava Kamma 17 - 18) where we have the disagreement between the Chachamim and Sumchos regarding the payment for the case of “pebbles.” The Chachamim maintain that the Halachah l’Moshe mi’Sinai teaches us that half damages are collected, whereas Sumchos disagrees.
The Maharitz Chayus quotes this question from the Chavos Yair (192), and suggests based on the Rambam in his explanation to a Mishna at the end of Eduyos that we have a tradition that Eliyahu Hanavi will do good for Klal Yisroel at the end of time, but there is a disagreement on the specifics. Here too, all agree that pebbles is a Halachah l’Moshe mi’Sinai that it is included in damages that one is responsible for, but they argue as to the extent of the liability.
The Gemora cites Rav Ashi inquiry: According to Sumchos, do we treat the damage caused by the force of the animal’s force the same way as the force of the animal itself? There are several approaches to understand this.
The Shitah Mekubetzes writes that since Sumchos does not agree that pebbles are learned from a Halachah l’Moshe mi’Sinai, the reason he holds that one is liable in full is purely based upon logic. Accordingly, there can be a distinction between damage caused by the animal’s force and damage caused by the force of the animal’s force.
The Rosh understands the inquiry as follows: Sumchos was uncertain if there was a Halachah l’Moshe mi’Sinai by pebbles at all. If there was one, perhaps it was coming to teach us that one is not liable to pay full damages by a case where the damage was caused by the force of the animal’s force; rather, he is only obligated to pay half.
According to both these approaches, it is evident that they did not learn like the Maharatz Chiyus.
Reb Avi Lebovitz quotes a Chasam Sofer (Beitzah 5a - pg. 20), who offers another approach. We certainly find many cases where there is a dispute regarding a Halachah l’Moshe mi’Sinai. The Rambam doesn’t mean to say that an argument cannot develop on a tradition; rather, he means to say that when there was a disagreement about a tradition and the Sages of the generation agree to one approach and reject the other – they essentially are deciding that the tradition of the one they accept is correct and the other is not. At that point, no later generation can restore the argument and rely on the tradition of the individual.