Does anyone know the size of the the set screw in the front diff cup? Part #25539 I assume that it is a 3x3mm or 4x4mm
Associated is sending me a new one, but I finally got some decent weather and would like to run to the hardware and get this part so I can finish the break in on my truck.

I believe it's the 3mm. Not 100% though. I just tightened mine 2 days ago, but just put the allen in and the one that worked, I tightened it with.

Mine was completely stripped from the factory. Associated has another one being sent to me, but I got some good weather and wanted to break this thing in. I ended up talking to several different guys at the LHS and they told me it was 4mm. Hopefully they are right because I picked one up from the local hardware store and I am getting ready to install now.

man, this must be an issue with these trucks. i lost mine this past weekend. at first it just seemed loose, but i reinstalled it, and it lasted maybe a full min, then tightened it again and gave more time for the thread lock to set and it looked like there was some sheared threads on the screw. it didn't last at all after that, and i lost the set screw. i need to order new diff cups.

I think it is a problem with the factory assembly. I ran a tank at idle, checked all the screws driveline motor etc. And both were loose in the front, when I tried to tighten one of them up it never did tighten up. I think hulk hogan must have been assembling mine at the factory because it had been way over tightened and was completely stripped.

what kind of lock tight should I use on the set screws?

I have heard that the blue works well and I have heard that some use the red. In this area I am not 100% sure, maybe one of the vets will see this and chime in.

I have been told that red locktite is PERMANENT.

Blue is Semi Permanent and used on 6mm or larger. Blue may be permanent on small screws like 2mm in size.

Purple locktite is for smaller than 6mm.

I picked up the blue and used it. This is on info from the LHS. They are 3mm set screws. And regular 3mm set screw will not work unless you grind a chamfer on the bottom of it.

red is "permanent" not PERMANENT!!! if you use a quality hex wrench, removing red loctite isn't much of a issue. if it won't budge without stripping the wrench or the screw, just heat it up with a little butane torch. im wrapping up a complete rebuild on my mgt and i used red on all the drivetrain set screws since backing out is such a problem.