I have changed out faulty isolators numerous times. Instead of putting isolators back in, I use a constant duty solenoid.
I wire the alternator feed directly to the start batteries(like original) and use the constant duty solenoid to feed to the house batteries. Use ignition switch power to trigger the solenoid, that way it only connects the house batteries when the engine is running.
When engine is off, the house batteries are completely on their own.
Been doing them this way for 30 years, no come backs
Constant duty solenoids are way cheaper and more reliable.
You can also get them almost anywhere.