I too just experienced this issue - in fact my '16 XLT EL with 45K is at the dealer now for repair as I write this.
I had been having what felt like light brake binding or drag on the left front wheel for the last 6 weeks or so. I felt it mostly when pulling out of my driveway: Start truck, foot on brake, put in drive, foot off brake, hit gas - felt like a shudder or grab in the front left wheel - lasted about 10 seconds then smooth sailing. Felt it whenever I took foot off brake (after being stopped) and hitting the gas to go. Took it to the dealer on June 13th for oil change and asked them to check out the issue with the wheel. They checked whole front end, drove the truck and didn't feel anything, could find nothing wrong - assured me truck was safe to drive.
Drove the truck for 2 weeks (200 miles) and still felt that annoying "grab", but assumed truck was safe. Went to grocery store last Tuesday, came out - started truck - got Low brake fluid warning. I thought this odd because the truck was just in for service the week before and they topped off all fluids - and there were no signs of a leak of any kind.I popped the hood and the brake fluid was well below the min line.
I drove home, parked the truck and made an appt with dealer for Saturday. Never took truck out again. Saturday, I go out to truck to go to appt - brake pedal to the floor! Pop hood - NO brake fluid, and no signs of leak. I call the mechanic up the road, he comes with brake fluid fills MC - and takes truck to his shop. Bleeds the brakes at all 4 wheels for $100 and calls me - brakes working fine - come pickup. I pick up truck - drive around the block an the brake fluid low warning light comes on again. I drive back to mechanic, he pops the hood and sees that the brake fluid is below min line and there is no sign of a leak. He says the MC has to be leaking into the brake booster.
I drove right to dealer (a white knuckle drive I might add), and left the truck there. They called yesterday to tell me they have to replace both the master cylinder and brake booster. They have ordered the parts and I should get my Expy back on Friday. I have an extended warranty - so the repair will only cost me a $100 co-pay. The scary thing is - if this failure happened to me on the highway - what a life changing disaster it could have been.
I suspect now that the MC was leaking into the brake booster for about six weeks - and that was what was causing the "drag/binding" feeling on that front left wheel. I just never considered that it could be a brake SYSTEM issue. This is something Expy owners need to be aware of.
