Susan, I did not direct my 2nd answer at you, rather at folks who have NEVER touched a brake pad or honed a wheel cylinder in their life. Armchair experts.
Corrosion seizing a disc brake caliper is SERIOUS. Rubber boots over the caliper piston are supped to SEAL the piston and the bore from moisture that can cause corrosion and seizing.
Corrosion can come from the inside. When CONDENSATION forms inside a master cylinder (the thing on the firewall, your brake pedal is connected to it) the condensation turns to water. Water is heavier than brake fluid so it gravitates its way down to wheel cylinders and calipers. Water also poisons the preservative value of brake fluid causing rubber sealing parts in the master cylinder and brake proportioning valve to DISINTEGRATE, and micro finished sealing bores in the metal to corrode and rust and seize parts. WATER also deteriorates brake HOSES, and you have hoses on the front wheels and of you have discs on each rear wheel. Drum rear brakes have a center hose down to the differential housing.
A frozen front disc is a warning sign. Similar to smoke coming from your battery bay.
Is there WATER inside the brake system? Destroying calipers, and master cylinder, hoses, and what not? You need a trustworthy independent inspection of this one single solitary point. If they FLUSH the brake system and capture WATER at the calipers and or wheel cylinders, it is time to think about passing this rig up or face a potential repair bill with a big comma in the price number.
I spent FOUR DAYS in Las Peñas Mexico, helping a rig owner overcome the effects (He was from Florida) of getting water in the brake system. Condensation from humid air.
Even though the brand new E-450 discs cost a measly seventy six dollars each (they are made in Mexico these days), with calipers, hoses, machining, master cylinder and proportioning valve, and my FREE labor, the job cost him more than six hundred dollars.
He was incredulous about water causing problems in the hoses, until I sliced one down the middle and peeled it open.
His rig was SIX YEARS OLD.
Water in the brake fluid is no joke. That is and was the point I was trying to make. I'll screw around with many systems, but steering, suspension and brakes.
Hope this helps
