Zest one side of the lime. Juice the grapefruit and lime and set those aside.
In the small bowl of the food processor, combine the garlic, grapefruit juice, lime zest and juice, 2 tablespoons of the oil, brown sugar, oregano, cumin, and salt. Process until blended.
Put the meat and the marinade in a vacuum-sealing bag. Close it up, and vacuum as much air as possible, then seal it. If you don't have a vacuum sealer, put the meat in a bag, get as much air out as possible, and put the bag, open side down, in a bowl.
Put the meat in the refrigerator for up to six hours.
To Make the Pork
When the pork has finished marinating, remove it from the marinade, but reserve it because you will be using it to make the sauce.
If you have a removable pot, do this part on the stovetop, otherwise, set the cooker to Saute. When the pot is hot, add the remaining oil. Add the pork to the pan and brown it on all sides. You may have to do this in batches to prevent boiling instead of browning. Keep the browned pieces in a bowl, so the juices don't get away.
Remove the pot from the stovetop, and return it to the Instant Pot or turn the unit off. Add the reserved marinade to the pot and scrape the bottom of the pot to release the fond. Then add the pork back to the pot with the bay leaf and wine. Cover the unit and make sure the vent is sealed. Set the cooker to 1 hour and 10 minutes or 70 minutes on high. When it is done, use Natural Release.
Remove the top of the cooker and carefully move the pork only to a large bowl. Keep the juices in the inner pot. Shred the meat using two forks. It will be hot, so unless you are using heatproof, waterproof gloves, don't use your fingers.
Remove the bay leaf from the sauce. You may use the saute function or remove it to the stovetop to thicken the sauce if you wish. Add a few tablespoons to the shredded pork and toss it, so all the pork gets a little sauce.
Serve the pork with corn tortillas, limes, cilantro, and fresh guacamole. Serve the sauce along side for dipping.
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