thanks for the feedback on the diff adjustment and the faulty shock cups.
i finally adjusted the diff 2 turns before full lock. it works fine.
about the shock cups though... i live in greece, so if i ask hpi for replacements, i'll probably get them by the time the pro5 is launched! so, i came up with a simple solution. i had a few spare shims, the kind you put on the outdrives to adjust the play of the diff in the housing. i put a silver and a coper one between the bladder and the plastic ball cup in all four shocks. now i can tighten them until i lock the plastic ball cup, as the sims fill the gap that was left between the cup and the bladder. very simple and effective.
it really s*cks though, when you get a "top of the line" car with defective parts and you have to think of ways to correct the manufacturer's mistakes