There is a glitch in his dialog that will allow you to continue gaining XP.
When you find him say:
-You were sent by Hsu.
-Concerned, you missed your check-in.
-What's the hold up?
Patch up his leg with a doc bag, send him back to the camp to get it looked at, and he should also give you a key.
Talk to Bryce back at Camp Mcarren (he wanders around):
-You were sent by Hsu.
-Concerned, you missed your check-in.
-What's the hold up?
-Let me take out Motor-Runner for you.
-[Speech 35] I can handle myself just fine.
Now everytime you talk to him back at the camp you'll recieve XP from the successful Speech influence.
I'm not 100% sure on my exact dialog choices while in vault 3. But here is a play-by-play of what I did incase those are off or missing some:
-I healed him and sent him back.
-he gave me the key to get to Motor-Runner.
-found and killed MR.
-returned to Hsu (did not have any active quests for him but recieved reward for returning Bryce).
-found Bryce (near the closest/largest tent upon exitting terminal).