The slider door on my 2014 Ram Promaster (2500-high roof, 136" wheel base) won't open from outside. Is this a common problem? The garage I bought it used from in May 2017 has tried repeatedly to fix it. Everytime he thinks it is fixed, it might work once or twice. Then the only way to open it is from inside. I plan to use this door as my main door while camping in it. I haven't started on a build-out because we can't get the door to open right from outside. Any idea?