Every time we asked the Guzzi expert about fixing the brakes his answer was "delink it" so we did.
Did brake lever control front and rear brakes ?
The front brake lever worked one front caliper. The rear pedal worked the other front caliper and the rear caliper. There's a proportion valve that controls the front/rear bias. The proportion valve tends to corrode inside and will reduce fluid pressure down to almost nothing.
When I tested it I coasted down towards the shop from the house. I was standing on the rear brake pedal and it didn't slow down at all. The proportion valve was plugged with corrosion.
We junked the proportion valve and had to replace the front master cylinder with a different bore size for dual calipers and the rear master cylinder with a bore for a single caliper. Then we got all new lines because the lengths had changed and rebuilt all three calipers.
A bike with Brembo brakes should stop good and now it does.