I had a leak at the fitting of the air pressure gage. On my coach the air lines all use press-on fittings that work like Chinese handcuffs in that you press the air line into the fitting and then pull back to set it. To remove the air line, use a wrench that just fits over it and press toward the fitting hard while wiggling the air line to release it. I had to install a new fitting which I got at NAPA.
My manual say to always extend or retract slides when the coach is at ride height. That means BEFORE the coach is leveled. Don't know if that is your problem or not, but it may be. What is the make, and year of your coach?