DBL, the D35 will hold up for many years, even with a locker. Yeah, I know, the prevaling thought is to not waste any money upgrading the D 35. But, consider the smallish tires he's running on his TJ. My thought is, as long as he stays committed to small tires, he's rarely going to have problems. I ran trails for several years that some of you guys only read about in four wheeling mags with the D 35 and a Detroit; and 33s and 35s. Yes, the tube housing eventually separated from the differential, and several times I had to change out axleshafts. I also recommend the locker be placed in the rear, my thought is that the rear axle does most of the work pushing the Jeep over the trail, almost all of the time. A locker will keep the rear tires pushing as long as one tire has traction. Just my thoughts, and I know there are some four wheelers that will disagree. You can just as easily snap an axleshaft if the locker is placed in the front axle. The problem with the D35 is the weak tube housing, and the C-clip.