Assuming the airport is not encrypted, the best way to do this is to open the .BGL file with ADE and fix the problematic parking spots yourself.
Or, alternatively, use ADE to create a new airport project starting from that .BGL, which you should be able to edit and compile using the official DevMode, which will also point you out to every kind of mistakes like isolated parking or unconnected links, etc.
Since there are already two viable ways to do that, using freely available tools, is not a very smart usage of our limited development time to add a 3rd to GSX, also considering if you left those errors in the .BGL, they would still affect AI workflow, that's why the proper way to fix obvious errors in airports is to fix the .BGL.
I'm shocked the hear there are paid products that won't fix the problem themselves: if they tried to recompile the scenery for any reason with the current version of the SDK DevMode, these errors will be flagged and the package won't even compile! That means the developer basically abandoned the scenery.
