Brakes losing preasure on 1992 Volkswagen Cabriolet

Hello, I just had the brakes redone, all new hardware, brakes and drums replaced in the rear. all new brakes and checked up front and new master cylinder and the brakes are still loosing preasure ( no leaks anywhere I've checked) when depresing the pedal it goes down and then will go down just a bit after that,, and the brakes will tighten up ( front only) on opccasion and can't figure out what it is. The only thing left is the brake booster and I am told it could not be this. Any sugestions ,, this one has got me.. I am wondering maybe the wrong brake fluid was put in it.

Asked by for the 1992 Volkswagen Cabriolet
From what you have described, major components of the brake system were replaced to include the rear wheel cylinders and master cylinder. From the symptom you describe it sounds like the system was not properly bleed eliminating all air from the system. This will cause sponginess in the brake pedal; I suggest you take the vehicle back to the shop that performed the service for a complete inspection and pressure test of the hydraulic system.
1 more answer , 1 more comment
have you checked your wheele cylinders in the back brakes
Sorry for the delay.
They were replaced as well. All new hardware on the rear.