I have a Greddy Blow Off Valve Kit Type S on my 89 T2.
A hybrid Turbo stage 2 pushing 14 pounds @5500rpms.
the BOV does not vent properly any more.

It is softer and longer in duration of relief.
My boost gauge is connected in to the vac line and it still reacts the same as when it was working correctly.
(ie 14pounds during boost and 22 VAC during decleration so this is a sign of no leakage..)

revs do not drop off as quick as they used to when it was funtioning correctly is another thing i noticed

(check sig for more mods.)

 

found the damn problem
a tear in the diaphram
check the pic out

i went out and bought another univerasl kit and did a vacume test on the new and the broken 1 ad the results are the same.