Ref my earlier note--this was one of several "recommended" solutions to cure/improve brake pedal pressure on the 2004 and newer coaches that employed the adjustable brake pedals. Thought was that changing out the 15w-40 for hyd fluid would improve pedal feel.
PS--the surest way I know of to get hydraulic hoses to leaking is to disconnect them. Rather than disconnecting and "blowing-out" the lines [opportunity for getting debris in lines], I'd advocate changing out the fluid in the reservoir and calling it good enough, swap it out a 2nd time if you like. Most petro-based fluids are pretty mixable; besides, if this process is good enough for the Allison conversion to Transynd, it's probably good enough for our hydraulics--IMHO.
2003 40' MDTS
Garden Ridge, Texas