GRENDEL1 posted at 8:29AM Sun, 27 December 2020 - #4408683

I did it by creating a master parameter dial that moved it in both world x and z simultaneously. It's not perfect, but it works pretty well....

That would be one way to go for it. It requires some trigonometric math and may not be robust to rotation of the parent object. A grouing like adp001 proposes is another, It requires setting the orientation of the axis of the group parallel to the rail. Easy to be done when the axis is in a world axis direction, May be more difficult when axis direction is different.
My quick and dirty solution would therefore be to add a constraint (special type of grouping) to the door with for target an object with centre at the other end of the rail (say the end doorpost). Works irrespectively of orienatation of the rail but of course you need to tune the location of the object origins.