I too have found it difficult to find someone competent to work on the campers -- gotta find an "OG"!
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Thanks for mentioning the brake booster and master cylinder (two things I didn't know existed!), as my newer camper does seem to have more of a mushy feeling. One mechanic "bled the lines" and one pulled off the tires and inspected the brakes, saying they were 60% and 80% and didn't need replacing. So that gives me two more things to mention to my new mechanic.
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Good luck with yours! Sue