It seems that tightening the cap too much is harder on the bladder than anything else. I just tighten mine to be just enough to be snug. No leakage and no blown bladders in both buggy and truggy. (OK, maybe a little tiny, wee bit of oil sneaks out but it's hardly noticable.)
The other problem people cause is overfilling the case and not letting the oil bleed out before tightening the cap.
Now that you mention it, I have to go and change the oil in my stock shocks.