Trasplanting a new brain into Rex (any of the three available will do) will cause a CTD right after the operation is done and you close the dialogue box telling you about the new capability Rex just got.

Seriously, by now I doubt this game was ever betatested.

Win7/64, quad core box on ATI Radeon.

Exact same problem here.

edit: I fixed the issue. In my case at least, the problem was my use of the adjustable timescale mod. As my timescale was different from the default 30, the bit where some time passes while the Doc transplants the brain must've caused the game some confusion. Setting the timescale to 30 for the quest end fixed it.

Interesting... My timescale is always 1, but then again that would still qualify as a bug, albeit of a different nature. I don't use any mods.

This quest did not bork for me, so I am wondering, did you put a Brain into Rex when he already had a brain transplant, or was this the first time?

I used the Fiend dogs brain that gives more speed on mine.

It was the first time for me, but I doubt that this matters much - I can confirm that setting timescale back to 30 solves both this and my other, similar problem related to staying overnight with Boone at Canyon 37.

Thanks much to Jimmah for the tip, now if only someone actually fixed it...