I had what thought was a valve lifter, but ended up to be a vacuum solenoid on the right bank under the alternator.
I would flush the complete brake fluid system and put in all new high temperature brake fluid.
Sounds like you went o a dealer. I do not care for dealers as they like to throw parts at a problem without fully diagnosing.
Bud
USAF Retired
Pace Arrow
2003 Chev Ice Road Tracker