You had the right idea with the Starport elevator, but you were pressing the wrong button. Press the one inside the elevator, you were actually looking at it at 44:13. Common mistake 😉 If you found Rachel's holotape before confronting Oswald, you would've had the option to tell him what happened. The end result would still be the same as the hard speech check, he'll leave peacefully after you give him her last recording. Since they glow, it's easier to look for those star cores in the evening when it's darker. Maybe check on the newly freed traders while you're looking for one, see how they're doing...
Love the insanity of the wasteland - get butted by a 2-headed bull in the first eight seconds, crash a raider/super mutant 'free-for-all' at 4 minutes, teleport through a fricken wall into power armour, gun down an entire town of ghouls, confirm that you were right about Rachel (yes, there is different dialogue - you can give Oswald the recording she made - it's a bit sad), go toe-to-toe with a mirelurk queen, take Jojo for an afternoon out at an amusement park, search for starcores (don't give up!), exterminate an infestation of giant bugs and rodents, and then meet the Hubologists. And you did it all with style. You've given Jojo a lot of great material to write his memoires when he grows up.
With the courser, you should just keep shooting him. Right now you're allied to the Institute, so they aren't hostile to you and they're willing to forgive getting shot a couple times. Just empty a magazine with something that shoots decently fast, like the Problem Solver, and he should turn hostile.
