I know nothing about the motorhome electrical system but everytime I hear about failures when using 12VDC would make me to insure the 12VDC feeding the motor was good.
Especially when you state it was working good for a coupe of weeks then slowly quit.
Perhaps the charging of the battery that provides power for the steps is not up to snuff... If the battery is down in charge you can always nose up a car battery to it and hookup some jumper cables...
Again I know nothing about the way motorhome's electrical systems are used - just a thought here...
Grinding of gears doesn't sound good however... Maybe low battery voltage caused that to happen when under load????
Roy Ken