Not corrosion -- corrosion would increase the resistance and decrease the current. (Could cause burning of the fuse contacts, though.)

Inspect the heavy wires attached to the fuse holder. In my '86 245, I discovered that the red insulation had cracked, and the bare copper wires were just a hair away from grounding.

If your car is a 240 in the range of '82 to '88, you might have a crumbling engine harness. (Before '82 no 25-amp fuse, after '88, Volvo used a better harness.)

When you step on the brakes, the engine might shift a bit, causing a bare wire in the harness to short to ground or another wire. Crumbling engine harnesses cause no end of weird symptoms.
--
Don Foster (near Cape Cod, MA)

Auto electrics is not my strong area. However, it is my belief that that fuse in inline with the feed to the fuel pump relay. If it were mine I would be cleaning the contact at the positive battery post, replacing the 25 amp holder and inspecting the fuelpump relay (you fail to mention what car you have). See if the connector to the relay is showing signs of being hot due to a high resistance connection. Just as a matter of good procedure I would resolder the printed circuit board in the relay. It takes a pretty good draw to blow a 25amp fuse so the source of the problem might very well show signs of heat when you look into the circuit.

Randy