Only this week, well yesterday fitted my new Collins diaphragm in my dv, old one kept sticking and all sorts.
It was acting a bit odd to start with, a bit lazy, but noticed it was not super flexible like the old one, which was now torn, and very mishapen.
After around 10 miles all good, hadn't realised it must have been leaking boost all the time, as it's defo pulling harder lower down from 1800rpm, and noticebaly faster all the way, one of those things that happens so slowly it doesn't get noticed, it laso idles better now, even with ignition smoothing off!!
Good luck with the boost hunt anyway,
tabetha