I had to replace my House battery disconnect switch a month or so ago. I found that it had no "click" and it had a large voltage drop across it (about 1 volt drop) unless I moved the knob a little then I could get it to make good contact. The House and Chassis switches are the same, except the labeling.
If your Coach starts with the Chassis disconnect switch off, then I expect the knob has broken free and its not actually turning the contact plate inside so it is always in the On position internally.
I replaced it with a new Blue Sea Systems "m-series" switch (as recommended on this forum) and it is a perfect fit. It comes in Red or Black
https://www.amazon.com/gp/product/B00445KFZ2/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1When I removed the old switch the "back fell off" and the contacts fell apart. It was only the battery cables pushing against the switch body that kept it from falling apart.
It was not hard to replace. On my coach I had to unbolt the Coach Power solenoid and move it slightly to get a socket on the battery stud. After that it was pretty easy.
This is what the old switch looked like when it came out (in two pieces). I plan to replace the Chassis disconnect switch too, just to be safe - but have not gotten to it yet.