I am running the EX1.5r and enjoying the car very capable.
You mentioned the drive shaft boots I am using these on the back of the car and they work well on the back and save filling the CVD with sand when running on Astro. After each run I just check they are pushed on ok. Just a note these boots do not fit the new Caster drive shafts with the smaller cups caster do not do an alternative for these shafts but apparently some team durango boots do i am waiting to receive a set of these.
I have had the same issue with the front lower arms broke one the same as you and managed to pull the pin ball from the lower arm. In both cases bad landings on a dirt track. I have had no issues with the car on the Astro. I have had these arms in the pan for a 1 hour simmer to softern them up. Were the arms you used MBX5 or 6? Also caster do a softer set of front arms not tried these.
The plastic part you have broken that aligns the front diff the 1.5r one is 7075 ali and i have had no issue with it.
As far as 74mm motor goes i have one sensored in my ex1.5r and it fits no problem.
I have had some issues with shells i would recommend slotting your holes because the flex in the chassis can split the shell.
One issue related to parts I am having is the upper hinge pins i bought a set as spare put they are to long spoken to the supplier and they have no record of the shorter pins on the EX1.5r so it looks like i will have to cut down the ones i have.
