Brake Booster

Hey peoples, i have recently noticed an issue with my booster.
1997 blazer 4dr 4.6L
Normally when the pedal is pressed down it will make that hiss sound then stop once the vacuum equalizes. Now i have found for about 3/4 of the pedal stroke, the hiss is continuous and continues to hiss unless i really lay into it. once the pedal is pretty much bottomed out it stops again as it would when working normally.

Vacuum to the booster is great and strong, there is no leak in the hose from intake to booster.

Braking quality is still good mind you i have noticed the pedal feels a little different depending on the stopping conditions.
Any ides, my only thoughts are there is a leak inside the booster.
Thanks in advance
Elliott

I have seen these boosters fill up with brake fluid that leaks out of the master cylinder due to a bad seal. Have you had to add brake fluid? You might be able to remove the vacuum line and look into the booster or carefully insert something like a pipe cleaner into the hole to see if there is brake fluid in the booster. Just be very careful not to rupture the diaphram inside the booster.

Hope this helps.