Your commitment to change from adversary to problem-solving partner can diffuse the long maintained tension. It's all in the attitude and intention.
Declare your intention to discuss the problem in a new way and your commitment to listen to what the other thinks and feels.
Make sure the time and place you will be listening is conducive to communicating. That means not at when others are with you, not while one of you is working (repairing the leaky faucet, cooking dinner), and turning off your phones.
Decide that this will be a time to learn how the other sees the problem and feels about it. It means putting aside your own perspective for just this time, and listening as if you were a friendly stranger.
Allow the other to speak without interrupting. If you are committed to hearing and learning, your focus will not be on arguing or planning your rebuttal.
Paraphrase what you've heard to clarify any misconceptions you may have and to show that you are genuinely listening. Ask meaningful, helpful questions that do not probe or make the speaker feel defensive.
Expect that initially you will hear a lot of emotion and hesitation. This has been an emotionally difficult problem for awhile and you will have to show you can be trusted to discuss it calmly. Listening with your attention, encouragement and occasional paraphrasing, the speaker may be able to move past the emotions and deeper into the substance of the problem.
If you've set aside your own perspective of the conflict in order to really listen to the other, you may even feel confident enough to wait until another time to present it. This can build trust that you will not attack and reassure the other that it will be safe to listen to you.
Marilyn Miller, MS, LPC ~ Psychotherapist
...Delighting every day in helping people find peace in their lives, relieving anxiety, depression, and promoting self-care.